Vibration motor

ABSTRACT

A vibration motor includes a base portion arranged to extend perpendicularly to a central axis extending in a vertical direction; a shaft; a coil portion; a bearing portion; a rotor holder; a magnet portion; and an eccentric weight. The base portion includes a base magnetic portion made of a magnetic metal; and a base nonmagnetic portion made of a nonmagnetic metal, fixed to an edge portion of the base magnetic portion, and arranged to extend from the edge portion of the base magnetic portion perpendicularly to the vertical direction. The base magnetic portion includes a plurality of magnetic element portions arranged in a circumferential direction, and arranged at positions opposed to the magnet portion in the vertical direction. The base nonmagnetic portion includes a plurality of nonmagnetic element portions arranged to alternate with the magnetic element portions in the circumferential direction, and arranged at positions opposed to the magnet portion in the vertical direction. The base magnetic portion includes a first boundary portion where the base magnetic portion is in contact with the base nonmagnetic portion. The base nonmagnetic portion includes a second boundary portion where the base nonmagnetic portion is in contact with the base magnetic portion. The base magnetic portion and the base nonmagnetic portion are arranged not to overlap with each other at any position outside of a boundary portion where the first and second boundary portions are in contact with each other when viewed in the vertical direction.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a vibration motor.

2. Description of the Related Art

Brushless vibration motors in the shape of a thin coin are typicallyused as silent notification devices in mobile communication apparatusesor the like, or for other purposes. JP-A 2009-130969 describes such avibration motor, in which a power supply flexible board 40 is fixed ontoa stator magnetic plate 10. Three cogging torque generating round holesh1 to h3, which are arranged in a circumferential direction, are definedin the stator magnetic plate 10. This prevents an annular magnet 50 fromstopping at a dead point, which would prohibit a rotating portion fromstarting rotating.

CN 204258531U discloses a technique of defining a base portion 11 by aninsert molding process using a magnetic body and a resin. In this case,the cogging torque generating round holes h1 to h3 as described aboveare not provided, but the resin, which is a non-magnetic material, isarranged to prevent an annular magnet 90 from stopping at a dead point.

When the size of a vibration motor is to be reduced, a reduction in thesize of a base portion is demanded. However, a reduction in the radialdimension of the stator magnetic plate 10 described in JP-A 2009-130969leads to an increase in the proportion of the total area of the coggingtorque generating round holes h1 to h3 to the area of the statormagnetic plate 10. This results in a reduction in the strength of thestator magnetic plate 10. In addition, the strength with which the powersupply flexible board 40 is fixed onto the stator magnetic plate 10 isalso reduced. According to the technique described in CN 204258531U, thebase portion 11 is defined by the insert molding process with themagnetic body and the resin placed one upon the other, and thisincreases the vertical thickness of the base portion 11, and thevertical dimension of the vibration motor.

SUMMARY OF THE INVENTION

A vibration motor according to a preferred embodiment of the presentinvention includes a base portion arranged to extend perpendicularly toa central axis extending in a vertical direction; a shaft having a lowerend fixed to the base portion, and arranged to project upward along thecentral axis; a circuit board arranged above the base portion; a coilportion attached to the circuit board, and arranged radially opposite tothe shaft with a gap therebetween; a bearing portion attached to theshaft to be rotatable with respect to the shaft above the coil portion;a rotor holder attached to the bearing portion; a magnet portionincluding a plurality of magnetic poles, and attached to the rotorholder; an eccentric weight attached to the rotor holder; and a coverportion arranged to cover, at least in part, upper and lateral sides ofthe rotor holder and the eccentric weight, and fixed to an upper end ofthe shaft and an outer edge portion of the base portion. The baseportion includes a base magnetic portion made of a magnetic metal; and abase nonmagnetic portion made of a nonmagnetic metal, fixed to an edgeportion of the base magnetic portion, and arranged to extend from theedge portion of the base magnetic portion perpendicularly to thevertical direction. The base magnetic portion includes a plurality ofmagnetic element portions arranged in a circumferential direction, andarranged at positions opposed to the magnet portion in the verticaldirection. The base nonmagnetic portion includes a plurality ofnonmagnetic element portions arranged to alternate with the magneticelement portions in the circumferential direction, and arranged atpositions opposed to the magnet portion in the vertical direction. Thebase magnetic portion includes a first boundary portion where the basemagnetic portion is in contact with the base nonmagnetic portion. Thebase nonmagnetic portion includes a second boundary portion where thebase nonmagnetic portion is in contact with the base magnetic portion.The base magnetic portion and the base nonmagnetic portion are arrangednot to overlap with each other at any position outside of a boundaryportion where the first and second boundary portions are in contact witheach other when viewed in the vertical direction.

The above preferred embodiment of the present invention is able toachieve a reduction in the thickness of the base portion.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vibration motor according to a firstpreferred embodiment of the present invention.

FIG. 2 is a vertical sectional view of the vibration motor.

FIG. 3 is a perspective view of a rotating portion and a stationaryportion of the vibration motor.

FIG. 4 is a perspective view of the stationary portion.

FIG. 5 is a plan view of the stationary portion.

FIG. 6 is a plan view of a base portion of the vibration motor.

FIG. 7 is a sectional view of a boundary portion between a base magneticportion and a base nonmagnetic portion according to the first preferredembodiment of the present invention.

FIG. 8 is a plan view of a magnet portion, a coil portion, and the baseportion according to the first preferred embodiment of the presentinvention.

FIG. 9 is a sectional view of a boundary portion between a base magneticportion and a base nonmagnetic portion according to a modification ofthe first preferred embodiment of the present invention.

FIG. 10 is a sectional view of a boundary portion between a basemagnetic portion and a base nonmagnetic portion according to amodification of the first preferred embodiment of the present invention.

FIG. 11 is a plan view of a stationary portion according to amodification of the first preferred embodiment of the present invention.

FIG. 12 is a plan view of a stationary portion according to amodification of the first preferred embodiment of the present invention.

FIG. 13 is a plan view of a stationary portion according to amodification of the first preferred embodiment of the present invention.

FIG. 14 is a plan view of a stationary portion according to amodification of the first preferred embodiment of the present invention.

FIG. 15 is a plan view of a stationary portion according to amodification of the first preferred embodiment of the present invention.

FIG. 16 is a plan view of a base portion according to a modification ofthe first preferred embodiment of the present invention.

FIG. 17 is a plan view of a magnet portion, a coil portion, and a baseportion according to a modification of the first preferred embodiment ofthe present invention.

FIG. 18 is a vertical sectional view of a vibration motor according to asecond preferred embodiment of the present invention.

FIG. 19 is a perspective view of a rotating portion and a stationaryportion of the vibration motor according to the second preferredembodiment of the present invention.

FIG. 20 is a vertical sectional view of a vibration motor according to athird preferred embodiment of the present invention.

FIG. 21 is a vertical sectional view of a vibration motor according to afourth preferred embodiment of the present invention.

FIG. 22 is a perspective view of a rotating portion and a stationaryportion of the vibration motor according to the fourth preferredembodiment of the present invention.

FIG. 23 is a perspective view of a stationary portion of a vibrationmotor according to a fifth preferred embodiment of the presentinvention.

FIG. 24 is a plan view of the stationary portion according to the fifthpreferred embodiment of the present invention.

FIG. 25 is a plan view of a base portion according to the fifthpreferred embodiment of the present invention.

FIG. 26 is a plan view of a magnet portion, a coil portion, and the baseportion according to the fifth preferred embodiment of the presentinvention.

FIG. 27 is a plan view of a magnet portion, a coil portion, and a baseportion according to a modification of the fifth preferred embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is assumed herein that a vertical direction is defined as a directionin which a central axis J1 of a vibration motor 1 extends, and that anupper side and a lower side along the central axis J1 in FIG. 2 arereferred to simply as an upper side and a lower side, respectively. Itshould be noted, however, that the above definitions of the verticaldirection and the upper and lower sides are not meant to indicaterelative positions or directions of different members or portions whenthose members or portions are actually installed in a device. It is alsoassumed herein that a direction parallel to the central axis J1 isreferred to as the vertical direction. Further, it is assumed hereinthat radial directions centered on the central axis J1 are simplyreferred to by the term “radial direction”, “radial”, or “radially”, andthat a circumferential direction about the central axis J1 is simplyreferred to by the term “circumferential direction”, “circumferential”,or “circumferentially”.

FIG. 1 is a perspective view illustrating the external appearance of thevibration motor 1 according to a first preferred embodiment of thepresent invention. FIG. 2 is a vertical sectional view of the vibrationmotor 1. Parallel oblique lines are omitted for sections of details inFIG. 2. In addition, in FIG. 2, features on the far side of the sectionof the vibration motor 1 are also depicted. FIG. 3 is a perspective viewof a rotating portion and a stationary portion of the vibration motor 1.FIG. 4 is a perspective view of the stationary portion of the vibrationmotor 1. FIG. 5 is a plan view of the stationary portion of thevibration motor 1. FIG. 6 is a plan view of a base portion 12.

The vibration motor 1 is a brushless motor in the shape of a coin. Thevibration motor 1 is used as, for example, a silent notification devicein a mobile communication apparatus, such as a cellular phone. In otherwords, the vibration motor 1 is included in the mobile communicationapparatus, for example.

The vibration motor 1 includes a cover portion 11 and the base portion12. The cover portion 11 is substantially in the shape of a coveredcylinder. The base portion 12 is substantially in the shape of a plate.The base portion 12 is arranged to extend perpendicularly to the centralaxis J1, which extends in the vertical direction. The cover portion 11is fixed to an outer edge portion of the base portion 12. The baseportion 12 is arranged to close a lower opening of the cover portion 11.The cover portion 11 is made of a metal. The base portion 12 is alsomade of a metal. The cover portion 11 and the base portion 12 areconnected to each other through, for example, welding. The base portion12 is arranged to have a thickness in the range of, for example, about0.1 mm to about 0.15 mm.

The vibration motor 1 further includes a circuit board 13, a coilportion 14, a shaft 15, a rotor holder 16, a magnet portion 17, and aneccentric weight 18. The vibration motor 1 further includes a bearingportion 21 and a spacer 22. The base portion 12, the circuit board 13,the coil portion 14, the shaft 15, and the spacer 22 are included in thestationary portion. The bearing portion 21, the rotor holder 16, themagnet portion 17, and the eccentric weight 18 are included in therotating portion. FIG. 3 illustrates the vibration motor 1 with thecover portion 11 removed therefrom. Each of FIGS. 4 and 5 illustratesthe vibration motor 1 with the cover portion 11 and the rotating portionremoved therefrom.

The base portion 12 includes a base projecting portion 121, a basemagnetic portion 122, and a base nonmagnetic portion 123. The basemagnetic portion 122 is made of a magnetic metal. The base magneticportion 122 is made of, for example, iron. The base nonmagnetic portion123 is made of a nonmagnetic metal. The base nonmagnetic portion 123 ismade of, for example, an austenitic stainless steel.

As illustrated in FIG. 6, the base magnetic portion 122 is substantiallyin the shape of an annular plate. The base nonmagnetic portion 123 isarranged radially inside of the base magnetic portion 122. The basenonmagnetic portion 123 is fixed to an edge portion of the base magneticportion 122. The base nonmagnetic portion 123 is arranged to extend fromthe edge portion of the base magnetic portion 122 substantiallyperpendicularly to the vertical direction. The base projecting portion121 is arranged to extend from the base magnetic portion 122 in adirection substantially perpendicular to the central axis J1. The baseprojecting portion 121 is arranged to project radially outward from thecover portion 11. In the preferred embodiment illustrated in FIG. 6, thebase projecting portion 121 and the base magnetic portion 122 aredefined by a single continuous monolithic member. The base projectingportion 121 is also made of a magnetic metal.

The base magnetic portion 122 includes a magnetic outer circumferentialportion 124 and a plurality of magnetic element portions 125. In thepreferred embodiment illustrated in FIG. 6, the base magnetic portion122 includes four magnetic element portions 125. The magnetic outercircumferential portion 124 is substantially annular. In more detail,the magnetic outer circumferential portion 124 is substantially in theshape of a circular ring, and is centered on the central axis J1. Themagnetic outer circumferential portion 124 is arranged to surround anouter periphery of the base nonmagnetic portion 123.

Each of the magnetic element portions 125 is defined integrally with themagnetic outer circumferential portion 124. Each of the magnetic elementportions 125 is arranged to project radially inward from the magneticouter circumferential portion 124. Each magnetic element portion 125 isa magnetic projecting portion arranged to project from an innercircumferential edge of the magnetic outer circumferential portion 124substantially perpendicularly to the vertical direction toward thecentral axis J1. Each of the magnetic element portions 125 is arrangedto have the same shape. The circumferential width of each of themagnetic element portions 125 is arranged to decrease in a radiallyinward direction.

The magnetic element portions 125 are arranged in the circumferentialdirection, and are arranged at positions opposed to the magnet portion17 in the vertical direction. The magnetic element portions 125 arearranged at equal angular intervals in the circumferential direction. Inthe preferred embodiment illustrated in FIG. 6, the four magneticelement portions 125 are arranged at intervals of 90 degrees. In otherwords, in a plan view, an angle defined between a straight line thatjoins a circumferential middle of each magnetic element portion 125 andthe central axis J1, and a straight line that joins a circumferentialmiddle of the magnetic element portion 125 adjacent thereto and thecentral axis J1, is 90 degrees.

The base nonmagnetic portion 123 includes a nonmagnetic central portion126 and a plurality of nonmagnetic element portions 127. In thepreferred embodiment illustrated in FIG. 6, the base nonmagnetic portion123 includes four nonmagnetic element portions 127. The nonmagneticcentral portion 126 is substantially in the shape of a disk, and iscentered on the central axis J1. A base central through hole 128, whichpasses through the base portion 12 in the vertical direction, is definedin a central portion of the nonmagnetic central portion 126. The basecentral through hole 128 is, for example, circular in a plan view.

Each of the nonmagnetic element portions 127 is defined integrally withthe nonmagnetic central portion 126. Each of the nonmagnetic elementportions 127 is arranged to project radially outward from thenonmagnetic central portion 126. Each nonmagnetic element portion 127 isa nonmagnetic projecting portion arranged to project from an outercircumferential edge of the nonmagnetic central portion 126substantially perpendicularly to the vertical direction. Each of thenonmagnetic element portions 127 is arranged to have the same shape. Thenonmagnetic element portions 127 are arranged to extend from thenonmagnetic central portion 126 in a radial manner with the central axisJ1 as a center. The circumferential width of each of the nonmagneticelement portions 127 is arranged to increase in a radially outwarddirection.

The nonmagnetic element portions 127 are arranged in the circumferentialdirection, and are arranged at positions opposed to the magnet portion17 in the vertical direction. The nonmagnetic element portions 127 arearranged at equal angular intervals in the circumferential direction. Inthe preferred embodiment illustrated in FIG. 6, the four nonmagneticelement portions 127 are arranged at intervals of 90 degrees. In otherwords, in a plan view, an angle defined between a straight line thatjoins a circumferential middle of each nonmagnetic element portion 127and the central axis J1, and a straight line that joins acircumferential middle of the nonmagnetic element portion 127 adjacentthereto and the central axis J1, is 90 degrees.

The nonmagnetic element portions 127 are arranged to alternate with themagnetic element portions 125 in the circumferential direction. Thecircumferential width of each magnetic element portion 125 is smallerthan the circumferential width of each nonmagnetic element portion 127at any radial position. The magnetic element portions 125 and thenonmagnetic element portions 127 are arranged at equal angular intervalsin the circumferential direction. In the preferred embodimentillustrated in FIG. 6, the four magnetic element portions 125 and thefour nonmagnetic element portions 127 are arranged at intervals of 45degrees. In other words, in a plan view, an angle defined between thestraight line that joins the circumferential middle of each magneticelement portion 125 and the central axis J1, and the straight line thatjoins the circumferential middle of the nonmagnetic element portion 127adjacent to the magnetic element portion 125 and the central axis J1, is45 degrees.

In FIG. 6, a first plane S1, which is an imaginary plane including thecentral axis J1 and a circumferential middle of the base projectingportion 121, is represented by a chain double-dashed line. In addition,a second plane S2, which is an imaginary plane including the centralaxis J1 and the circumferential middle of one of the magnetic elementportions 125 that is closest to the first plane S1 in thecircumferential direction of all the magnetic element portions 125, isalso represented by a chain double-dashed line. In FIG. 6, the magneticelement portion 125 in the upper left of the figure is regarded as thisone of the magnetic element portions 125. An angle A3 defined betweenthe first plane S1 and the second plane S2 is, for example, 45 degrees.

The base magnetic portion 122 includes a first boundary portion 122 a,which is an area where the base magnetic portion 122 is in contact withthe base nonmagnetic portion 123. The base nonmagnetic portion 123includes a second boundary portion 123 a, which is an area where thebase nonmagnetic portion 123 is in contact with the base magneticportion 122. An area where the first boundary portion 122 a and thesecond boundary portion 123 a are in contact with each other is definedas a boundary portion 120. In more detail, at the boundary portion 120,the base magnetic portion 122 and the base nonmagnetic portion 123 arearranged to be in contact with each other substantially over the entirelength thereof. A side edge of each magnetic element portion 125 isarranged to be in contact with a side edge of an adjacent one of thenonmagnetic element portions 127, each side edge extending substantiallyin a radial direction. An inner edge of each magnetic element portion125, the inner edge extending substantially in the circumferentialdirection, is arranged to be in contact with an outer circumferentialedge of the nonmagnetic central portion 126. An outer edge of eachnonmagnetic element portion 127, the outer edge extending substantiallyin the circumferential direction, is arranged to be in contact with theinner circumferential edge of the magnetic outer circumferential portion124.

The base magnetic portion 122 and the base nonmagnetic portion 123 arewelded to each other at the boundary portion 120 between the basemagnetic portion 122 and the base nonmagnetic portion 123, and are thusfixed to each other. The base magnetic portion 122 and the basenonmagnetic portion 123 are welded to each other at, for example, aplurality of separate positions along the boundary portion 120. Notethat the base magnetic portion 122 and the base nonmagnetic portion 123may alternatively be welded to each other at the boundary portion 120substantially over the entire length thereof. Also note that the basemagnetic portion 122 and the base nonmagnetic portion 123 may notnecessarily be fixed to each other through welding, but mayalternatively be fixed to each other through, for example, adhesion orpress fitting.

The base magnetic portion 122 and the base nonmagnetic portion 123 donot overlap with each other at any position outside of the boundaryportion 120, which is the area where the first boundary portion 122 aand the second boundary portion 123 a are in contact with each other,when viewed in the vertical direction. In other words, no portion of thebase magnetic portion 122 is arranged over or under the base nonmagneticportion 123 at any position outside of the boundary portion 120.

FIG. 7 is a sectional view illustrating the boundary portion 120 betweenthe base magnetic portion 122 and the base nonmagnetic portion 123 in anenlarged form. In FIG. 7, a section of a portion of the boundary portion120 of the base portion 12 at which the base magnetic portion 122 andthe base nonmagnetic portion 123 are not welded to each other is shown.Except where the base magnetic portion 122 and the base nonmagneticportion 123 are welded to each other, the boundary portion 120 has asection similar to the section illustrated in FIG. 7.

In the embodiment illustrated in FIG. 7, the base magnetic portion 122and the base nonmagnetic portion 123 do not overlap with each other evenat the boundary portion 120 when viewed in the vertical direction. Inmore detail, the base magnetic portion 122 and the base nonmagneticportion 123 do not overlap with each other when viewed in the verticaldirection where the base magnetic portion 122 and the base nonmagneticportion 123 are not welded to each other in the boundary portion 120.Note that, where the base magnetic portion 122 and the base nonmagneticportion 123 are welded to each other, portions of both the base magneticportion 122 and the base nonmagnetic portion 123 are mixed as a resultof fusion, which may make it unclear whether the base magnetic portion122 and the base nonmagnetic portion 123 overlap with each other whenviewed in the vertical direction. A side surface of the edge portion ofthe base magnetic portion 122 is arranged to be parallel orsubstantially parallel to the vertical direction, and a side surface ofan edge portion of the base nonmagnetic portion 123 is also arranged tobe parallel or substantially parallel to the vertical direction. Theside surface of the edge portion of the base magnetic portion 122 andthe side surface of the edge portion of the base nonmagnetic portion 123are arranged opposite to and in contact with each other in a directionperpendicular to the vertical direction.

The base magnetic portion 122 is arranged to have a vertical thicknesssubstantially equal to the vertical thickness of the base nonmagneticportion 123. Regarding an upper surface of the base portion 12, an uppersurface 31 of the base magnetic portion 122 and an upper surface 33 ofthe base nonmagnetic portion 123 are arranged at the same vertical levelsubstantially over the entire upper surface of the base portion 12. Inaddition, regarding a lower surface of the base portion 12, a lowersurface 32 of the base magnetic portion 122 and a lower surface 34 ofthe base nonmagnetic portion 123 are arranged at the same vertical levelsubstantially over the entire lower surface of the base portion 12.

The circuit board 13 is arranged on the base portion 12. A centralportion of the circuit board 13 includes a board central through hole131 through which the shaft 15 is inserted. The board central throughhole 131 is, for example, circular in a plan view. The circuit board 13is arranged to cover substantially the entire upper surface of the baseportion 12 except an outer edge portion of the upper surface of the baseportion 12. Over an area where the upper surface of the base portion 12is covered with the circuit board 13, the upper surface 31 of the basemagnetic portion 122 and the upper surface 33 of the base nonmagneticportion 123 are arranged at the same vertical level as mentioned above.The circuit board 13 is fixed to the base portion 12 through anadhesive, for example. Note that the concept of “adhesive” in thepresent preferred embodiment includes a double-sided tape, glue, and soon. The circuit board 13 is a flexible printed circuit (FPC) board,which has flexibility. An electronic component 24 is attached onto thecircuit board 13. The electronic component 24 is arranged to detectrotation of the magnet portion 17, for example. The electronic component24 is, for example, a Hall sensor. The electronic component 24 mayalternatively be a capacitor, a resistor, or any of various othercomponents.

The coil portion 14 is attached onto the circuit board 13. The coilportion 14 is electrically connected to the circuit board 13. In thepreferred embodiment illustrated in FIGS. 2 to 5, the coil portion 14 isdefined by a single annular coil 141. The shaft 15 is arranged inside ofthe coil 141. The coil 141 is fixed onto the circuit board 13 through anadhesive, for example.

The coil 141 is, for example, substantially in the shape of arectangular ring, elongated in one radial direction in a plan view. Thecoil 141 includes two long side portions 145 and two short side portions146. Each of the two long side portions 145 is arranged to extend in alongitudinal direction of the coil 141 with the shaft 15 arrangedbetween the two long side portions 145. The two short side portions 146are arranged to join both end portions of the two long side portions145. Each of the two short side portions 146, which is a radially outerend portion of the coil 141, is arranged above the magnetic outercircumferential portion 124 of the base portion 12, and is arranged tooverlap with the magnetic outer circumferential portion 124 when viewedin the vertical direction. In addition, the radially outer end portionof the coil 141 is arranged radially outward of an outer circumferentialedge of the magnet portion 17. Note that the radially outer end portionof the coil 141 may alternatively be arranged radially inward of theouter circumferential edge of the magnet portion 17.

In the preferred embodiment illustrated in FIG. 5, the width of aninterspace between the two long side portions 145 is arranged to besmaller on one side (i.e., the left side in the figure) of alongitudinal middle of the coil 141 than on the other side (i.e., theright side in the figure) of the longitudinal middle. The width of theinterspace between the two long side portions 145 refers to the distancebetween the two long side portions 145 as measured in a directionperpendicular to the longitudinal direction of the coil 141. In moredetail, on the left side of the longitudinal middle of the coil 141 inFIG. 5, the width of the interspace between the long side portions 145is arranged to gradually decrease with increasing distance from thelongitudinal middle. In addition, on the right side of the longitudinalmiddle of the coil 141 in FIG. 5, the width of the interspace betweenthe long side portions 145 is arranged to be substantially uniformregardless of the distance from the longitudinal middle. Therefore, theshort side portion 146 on the left side of the longitudinal middle ofthe coil 141 is shorter than the short side portion 146 on the rightside of the longitudinal middle of the coil 141.

In FIG. 5, a coil middle plane S5, which is an imaginary plane parallelto the longitudinal direction of the coil 141 and including the centralaxis J1, is represented by a chain double-dashed line. An angle A2defined between the coil middle plane S5 and the first plane S1 is, forexample, 22.5 degrees. Each of the two long side portions 145 of thecoil 141 extends along the coil middle plane S5. In more detail, thelong side portion 145 on the lower side in FIG. 5 is parallel to thecoil middle plane S5 substantially over the entire length thereof. Thelong side portion 145 on the upper side in FIG. 5 is parallel to thecoil middle plane S5 on the right side of the longitudinal middle of thecoil 141. In addition, on the left side of the longitudinal middle ofthe coil 141, the long side portion 145 on the upper side is arranged togradually approach the coil middle plane S5 with increasing distancefrom the longitudinal middle.

On the left side in FIG. 5, which is the aforementioned one side, of thelongitudinal middle of the coil 141, the electronic component 24 isattached onto the circuit board 13 at a position near the long sideportion 145 on the upper side in FIG. 5, which is one of the long sideportions 145 of the coil 141. The electronic component 24 is arrangedadjacent to the aforementioned long side portion 145 and outside of thecoil 141. In the preferred embodiment illustrated in FIG. 5, theelectronic component 24 is arranged adjacent to the coil 141 on theupper side of the long side portion 145 on the upper side in the figure.

An angle A1 defined between a component middle plane S6, which is animaginary plane passing through the electronic component 24 andincluding the central axis J1, and the coil middle plane S5, whichpasses through the short side portions 146 of the coil 141 and includesthe central axis J1, is, for example, 45 degrees. Each short sideportion 146 is a longitudinal end portion of the coil 141. In moredetail, the coil middle plane S5 includes the central axis J1 and acircumferential middle of one of the short side portions 146 which iscloser to the base projecting portion 121. Meanwhile, the componentmiddle plane S6 includes the central axis J1 and a circumferentialmiddle of the electronic component 24. The aforementioned angle A1 maynot necessarily be precisely 45 degrees, but may be practically 45degrees. Note that the aforementioned angle A1 may be appropriatelychanged to an angle other than 45 degrees. The arrangement of the coil141 and the electronic component 24 may be modified appropriately. Forexample, the coil 141 and the electronic component 24 may be arranged atpositions rotated 45 degrees in a counterclockwise direction about thecentral axis J1 from the respective positions thereof illustrated inFIG. 5.

Lead wires 147 extending from the coil 141 are connected to the circuitboard 13 on the opposite side of the coil 141 with respect to theelectronic component 24. In other words, each lead wire 147 is connectedto the circuit board 13 at a position closer not to the long sideportion 145 near which the electronic component 24 is arranged but tothe other long side portion 145. In the preferred embodiment illustratedin FIG. 5, each lead wire 147 is connected to the circuit board 13 at aposition near the coil 141 on the lower side of the long side portion145 on the lower side in the figure. In FIG. 5, a connection portion 147a at which each lead wire 147 is connected to the circuit board 13 ishatched with parallel oblique lines. The lead wire 147 is connected tothe circuit board 13 through, for example, soldering. Note that the leadwire 147 may alternatively be connected to the circuit board 13 by amethod other than soldering. Also note that the connection portion 147 amay not necessarily be arranged on the opposite side of the coil 141with respect to the electronic component 24, but may alternatively bearranged at another appropriate position.

The shaft 15 is arranged to have the central axis J1 as a centerthereof. A lower end of the shaft 15 is fixed to the base portion 12.Specifically, the lower end of the shaft 15 is fixed in the base centralthrough hole 128. For example, the lower end of the shaft 15 is pressfitted in the base central through hole 128, and is welded to the basenonmagnetic portion 123. A lower end surface of the shaft 15 is arrangedat the same vertical level as that of a portion of the lower surface ofthe base portion 12 which is near and around the base central throughhole 128.

An upper surface of an entire portion of the base portion 12 which liesbetween the shaft 15 and an inner circumferential edge of the coil 141in a plan view is arranged at the same vertical level. Moreover, anupper surface of an entire portion of the base portion 12 which liesbetween the shaft 15 and the magnetic element portions 125 and thenonmagnetic element portions 127 is arranged at the same vertical level.In other words, the upper surface 33 of the nonmagnetic central portion126, which defines a portion of the upper surface of the base portion 12between the base central through hole 128 and the magnetic elementportions 125 and the nonmagnetic element portions 127, is a flat surfaceperpendicular to the vertical direction substantially in its entirety.

The shaft 15 is arranged to project upward from the base portion 12along the central axis J1. An upper end of the shaft 15 is fixed to acentral portion of a top cover portion of the cover portion 11. Theshaft 15 is fixed to the cover portion 11 through, for example, weldingand press fitting. The shaft 15 is arranged radially opposite to thecoil 141 with a gap therebetween. In other words, the coil portion 14 isarranged radially opposite to the shaft 15 with the gap therebetween. Nomember of the vibration motor 1 is arranged in this gap. The shaft 15 ismade of, for example, a metal. Note that the shaft 15 may alternativelybe made of another material.

The base portion 12 includes a base peripheral through hole 129, whichpasses through the base portion 12 in the vertical direction, at aposition away from the shaft 15. In the preferred embodiment illustratedin FIG. 6, the base peripheral through hole 129 is defined in the basenonmagnetic portion 123, the outer periphery of which is surrounded bythe base magnetic portion 122. The circuit board 13 includes a boardperipheral through hole 132, which is arranged to overlap with the baseperipheral through hole 129 of the base portion 12 when viewed in thevertical direction. The base peripheral through hole 129 is, forexample, in the shape of a circle or polygon in a plan view. The boardperipheral through hole 132 is also, for example, in the shape of acircle or polygon in a plan view. The base peripheral through hole 129and the board peripheral through hole 132 are preferably arranged tohave the same shape.

Each of the base peripheral through hole 129 and the board peripheralthrough hole 132 is used when assembling the vibration motor 1.Specifically, a jig in the shape of a pin is inserted through the baseperipheral through hole 129 when the circuit board 13 is fixed to thebase portion 12. The shaft 15 is fixed in the base central through hole128 beforehand. Then, the aforementioned jig is inserted through theboard peripheral through hole 132, while the shaft 15 is insertedthrough the board central through hole 131 of the circuit board 13.Thereafter, the circuit board 13 is fixed to the upper surface of thebase portion 12 through the adhesive or the like, and the jig isremoved.

As described above, in the vibration motor 1, at the position away fromthe shaft 15, the base peripheral through hole 129 is defined in thebase portion 12, and the board peripheral through hole 132, whichoverlaps with the base peripheral through hole 129 when viewed in thevertical direction, is defined in the circuit board 13. Then, the shaft15 and the jig are inserted through the board central through hole 131and the board peripheral through hole 132, respectively, of the circuitboard 13 to improve positional precision with which the circuit board 13is attached to the base portion 12.

The base peripheral through hole 129 is defined in the base nonmagneticportion 123, the outer periphery of which is surrounded by the basemagnetic portion 122, as described above. The base peripheral throughhole 129 is thus defined at a position away from the outer edge portionof the base portion 12, and this contributes to limiting a reduction instrength of the base portion 12 caused by the base peripheral throughhole 129.

The spacer 22 is a substantially annular plate-shaped member including athrough hole defined in a center thereof. In the preferred embodimentillustrated in FIGS. 4 and 5, the spacer 22 is in the shape of acircular ring, and is centered on the central axis J1. Note that thespacer 22 may alternatively be, for example, in the shape of the letter“C”, that is, a circular ring with one circumferential portion omitted.The shaft 15 is inserted through the through hole of the spacer 22. Thespacer 22 is attached to the shaft 15 through, for example, pressfitting. The spacer 22 is arranged above the coil portion 14, and isfixed to the shaft 15. The spacer 22 is made of, for example, a resin.Note that the spacer 22 may alternatively be made of another material.Also note that the spacer 22 may alternatively be attached to the shaft15 by a method other than press fitting.

A lower surface 221 of the spacer 22 is arranged opposite to an uppersurface 142 of the coil 141 of the coil portion 14 in the verticaldirection. In the preferred embodiment illustrated in FIG. 4, the lowersurface 221 of the spacer 22 is arranged to be in contact with the uppersurface 142 of the coil 141 of the coil portion 14.

The bearing portion 21 is an annular member including a through holedefined in a center thereof. In the preferred embodiment illustrated inFIG. 2, the bearing portion 21 includes a substantially cylindricalportion centered on the central axis J1, and a portion substantially inthe shape of a semicircular disk and arranged to project to the left inFIG. 2 from an upper portion of the substantially cylindrical portion.The shaft 15 is inserted through the through hole of the bearing portion21. The bearing portion 21 is attached to the shaft 15 to be rotatablewith respect to the shaft 15 above the coil 141 of the coil portion 14.In addition, the bearing portion 21 is arranged above the spacer 22. Inother words, the spacer 22 is attached to the shaft 15 between thebearing portion 21 and the coil 141 of the coil portion 14.

As illustrated in FIG. 2, an upper surface 223 of the spacer 22 isarranged to be in contact with a lower surface 211 of the bearingportion 21. In the preferred embodiment illustrated in FIG. 2, an outeredge of the upper surface 223 of the spacer 22 is arranged tosubstantially coincide with an outer edge of the lower surface 211 ofthe bearing portion 21 in its entirety. In other words, the uppersurface 223 of the spacer 22 is arranged to have an outside diametersubstantially equal to the outside diameter of the lower surface 211 ofthe bearing portion 21. The bearing portion 21 is a plain bearing. Notethat the bearing portion 21 may alternatively be a bearing of anothertype. The bearing portion 21 is made of, for example, a sintered metal.Preferably, the bearing portion 21 is impregnated with a lubricatingoil. Note that the bearing portion 21 may alternatively be made ofanother material.

The rotor holder 16 is a member substantially in the shape of a coveredcylinder. The rotor holder 16 is attached to the bearing portion 21. Inmore detail, an inner circumferential portion of a top cover portion ofthe rotor holder 16 is fixed to, for example, an outer circumferentialportion of the bearing portion 21. The rotor holder 16 is thus supportedby the bearing portion 21 to be rotatable with respect to the shaft 15.The rotor holder 16 is made of, for example, a metal.

The magnet portion 17 is a member substantially in the shape of acircular ring, and is centered on the central axis J1. The magnetportion 17 is attached to the rotor holder 16. In more detail, an uppersurface of the magnet portion 17, which is substantially cylindrical, isattached to a lower surface of the top cover portion of the rotor holder16. The magnet portion 17 is arranged above the coil 141 of the coilportion 14, and is arranged opposite to the coil 141 in the verticaldirection with a gap therebetween. The magnet portion 17 is arrangedaround the bearing portion 21. The bearing portion 21 is arrangedradially inside of the magnet portion 17. An inner circumferentialsurface of the magnet portion 17 is fixed to an outer circumferentialsurface of the bearing portion 21.

In the preferred embodiment illustrated in FIG. 2, the eccentric weight18 is arranged to have a shape corresponding to that of a right half ofa substantially cylindrical member. The eccentric weight 18 issubstantially semicircular in a plan view. The eccentric weight 18 isattached to the rotor holder 16. In more detail, a lower surface of theeccentric weight 18 is attached to an upper surface of the top coverportion of the rotor holder 16 through, for example, an adhesive. Thecenter of gravity of the eccentric weight 18 is radially away from thecentral axis J1.

The cover portion 11 is arranged to cover upper and lateral sides of therotor holder 16 and the eccentric weight 18. The cover portion 11 maynot necessarily cover the rotor holder 16 and the eccentric weight 18 intheir entirety. The cover portion 11 may include an opening or the likedefined therein, as long as the cover portion 11 is arranged to cover,at least in part, the rotor holder 16 and the eccentric weight 18. Thecover portion 11 is fixed to the upper end of the shaft 15, and is alsofixed to the outer edge portion of the base portion 12, as describedabove.

In the vibration motor 1, an electric current is supplied to the coil141 of the coil portion 14 through the circuit board 13 to generate atorque between the coil 141 and the magnet portion 17. The rotatingportion, that is, a combination of the bearing portion 21, the rotorholder 16, the magnet portion 17, and the eccentric weight 18, is thuscaused to rotate around the shaft 15. In the coil portion 14, a portionof the coil 141 which extends substantially in a radial direction is atorque generating portion that causes the torque to be generated betweenthe magnet portion 17 and the coil 141. In the preferred embodimentillustrated in FIGS. 4 and 5, each of the two long side portions 145 ofthe coil 141 is the torque generating portion. Since the center ofgravity of the eccentric weight 18 is radially away from the centralaxis J1 as described above, the rotation of the eccentric weight 18causes vibrations. If the supply of the electric current to the coilportion 14 is stopped, the rotation of the rotating portion stops. Whenthe rotation of the rotating portion stops, a plurality of magneticpoles 171 of the magnet portion 17 stop at predetermined circumferentialstop positions.

FIG. 8 is a diagram illustrating an example stop position of the magnetportion 17. FIG. 8 is a plan view illustrating the magnet portion 17,the coil portion 14, and the base portion 12. In FIG. 8, for easierunderstanding of the positional relationships between the magnet portion17, the coil portion 14, and the magnetic element portions 125 of thebase portion 12, the other components, including the circuit board 13,are not shown.

The magnet portion 17 includes the plurality of magnetic poles 171. Thenumber of magnetic poles 171 is, for example, a multiple of two.Preferably, the number of magnetic poles 171 is a multiple of four. Inthe preferred embodiment illustrated in FIG. 8, the magnet portion 17includes four magnetic poles 171. That is, the magnet portion 17includes two north poles and two south poles. The two north poles andthe two south poles are arranged to alternate with each other in thecircumferential direction. The magnetic poles 171 are arranged at equalangular intervals in the circumferential direction. In the preferredembodiment illustrated in FIG. 8, the four magnetic poles 171 arearranged at intervals of 90 degrees. In other words, in a plan view, anangle defined between a straight line that joins a circumferentialmiddle of each magnetic pole 171 and the central axis J1, and a straightline that joins a circumferential middle of the magnetic pole 171adjacent thereto and the central axis J1, is 90 degrees.

The number of magnetic element portions 125 of the base portion 12 ispreferably equal to or smaller than the number of magnetic poles 171. Inthe preferred embodiment illustrated in FIG. 8, the number of magneticelement portions 125 is equal to the number of magnetic poles 171. Asdescribed above, the magnetic element portions 125 are arranged at equalangular intervals in the circumferential direction, and the magneticpoles 171 are also arranged at equal angular intervals in thecircumferential direction. Therefore, in the preferred embodimentillustrated in FIG. 8, both the magnetic element portions 125 and themagnetic poles 171 are arranged at the same angular intervals of 90degrees in the circumferential direction.

A radially inner end portion of each of the magnetic element portions125 is arranged opposite to the magnet portion 17 in the verticaldirection. The circumferential width of a portion of the magneticelement portion 125 which is opposed to the magnet portion 17 in thevertical direction is equal to or smaller than the circumferential widthof each magnetic pole 171 of the magnet portion 17 at any radialposition. In the preferred embodiment illustrated in FIG. 8, thecircumferential width of the portion of the magnetic element portion 125which is opposed to the magnet portion 17 in the vertical direction issmaller than the circumferential width of each magnetic pole 171 of themagnet portion 17 at any radial position.

In the vibration motor 1, once the supply of the electric current to thecoil 141 of the coil portion 14 is stopped, cogging torque generatedbetween the magnetic element portions 125 of the base magnetic portion122 and the magnet portion 17 causes the rotating portion to stop witheach of the magnetic poles 171 of the magnet portion 17 positioned overone of the magnetic element portions 125. In more detail, the rotatingportion is caused to stop with the circumferential middle of eachmagnetic pole 171 positioned opposite to the circumferential middle ofone of the magnetic element portions 125 in the vertical direction. Inthe preferred embodiment illustrated in FIG. 8, the circumferentialmiddle of each of the four magnetic poles 171 coincides with thecircumferential middle of a separate one of the four magnetic elementportions 125 when viewed in the vertical direction.

As described above, the angle A3 defined between the first plane S1,which includes the central axis J1 and the circumferential middle of thebase projecting portion 121, and the second plane S2, which includes thecentral axis J1 and the circumferential middle of the magnetic elementportion 125, is 45 degrees. In addition, the angle A2 defined betweenthe first plane S1 and the coil middle plane S5 is 22.5 degrees.Therefore, an angle defined between the coil middle plane S5 and thesecond plane S2 is 22.5 degrees. Therefore, when the rotating portion isin a stopped state, the circumferential middle of the magnetic pole 171that overlaps with the magnetic element portion 125 near the coil middleplane S5 when viewed in the vertical direction is displaced from thecoil middle plane S5 in the circumferential direction by 22.5 degrees.

In the coil 141, each of the two long side portions 145, which is thetorque generating portion that causes a torque to rotate the rotatingportion to be generated between the magnet portion 17 and the coil 141,extends along the coil middle plane S5 as described above. This allowsthe circumferential middle of each magnetic pole 171 of the magnetportion 17 to be displaced from each of the two long side portions 145in the circumferential direction when the rotating portion is in thestopped state. In other words, each magnetic pole 171 is prevented frombeing positioned at a dead point, which would prohibit the rotatingportion from starting rotating, when the rotating portion is in thestopped state. The angle defined between the coil middle plane S5 andthe second plane S2 mentioned above is preferably 90 degrees divided bythe number of magnetic poles 171.

As described above, the vibration motor 1 includes the base portion 12,the shaft 15, the circuit board 13, the coil portion 14, the bearingportion 21, the rotor holder 16, the magnet portion 17, the eccentricweight 18, and the cover portion 11. The base portion 12 is made of themetal. This contributes to reducing the thickness of the base portion12, that is, reducing the vertical dimension of the vibration motor 1,while limiting a reduction in the strength of the base portion 12.

The base portion 12 includes the base magnetic portion 122 made of themagnetic metal, and the base nonmagnetic portion 123 made of thenonmagnetic metal. The base nonmagnetic portion 123 is fixed to the edgeportion of the base magnetic portion 122, and extends from the edgeportion of the base magnetic portion 122 perpendicularly to the verticaldirection. The base magnetic portion 122 includes the magnetic elementportions 125. The magnetic element portions 125 are arranged in thecircumferential direction, and are arranged at the positions opposed tothe magnet portion 17 in the vertical direction. The base nonmagneticportion 123 includes the nonmagnetic element portions 127. Thenonmagnetic element portions 127 are arranged to alternate with themagnetic element portions 125 in the circumferential direction, and arearranged at the positions opposed to the magnet portion 17 in thevertical direction. This contributes to preventing each magnetic pole171 of the magnet portion 17 from being positioned at any dead pointwhen the rotating portion is in the stopped state as described above.

The base magnetic portion 122 and the base nonmagnetic portion 123 donot overlap with each other at any position outside of the boundaryportion when viewed in the vertical direction. This allows the baseportion 12 to have a smaller thickness than in the case where the basemagnetic portion 122 and the base nonmagnetic portion 123 overlap witheach other at a position other than the boundary portion 120. This leadsto a reduced thickness of the vibration motor 1.

As illustrated in FIG. 7, in the base portion 12, the base magneticportion 122 and the base nonmagnetic portion 123 do not overlap witheach other even at the boundary portion 120 when viewed in the verticaldirection. This contributes to a further reduction in the thickness ofthe base portion 12. This in turn leads to a further reduction in thethickness of the vibration motor 1. In addition, each of the sidesurface of the edge portion of the base magnetic portion 122 and theside surface of the edge portion of the base nonmagnetic portion 123 isarranged to be substantially parallel to the vertical direction, andthis makes it easier to define the edge portion of the base magneticportion 122 and the edge portion of the base nonmagnetic portion 123.This makes it easier to manufacture the base portion 12.

As described above, over the area where the upper surface of the baseportion 12 is covered with the circuit board 13, the upper surface ofthe base magnetic portion 122 and the upper surface of the basenonmagnetic portion 123 are arranged at the same vertical level. Thisallows the circuit board 13 to be securely fixed to the upper surface ofthe base portion 12. In addition, the lower surface of the base magneticportion 122 and the lower surface of the base nonmagnetic portion 123are also arranged at the same vertical level. This prevents a projectingportion from being defined in the lower surface of the base portion 12.This contributes to a further reduction in the thickness of the baseportion 12. This in turn leads to a further reduction in the thicknessof the vibration motor 1.

In the vibration motor 1, the base magnetic portion 122 and the basenonmagnetic portion 123 may overlap with each other at the boundaryportion 120 when viewed in the vertical direction. Each of FIGS. 9 and10 is a sectional view illustrating a boundary portion 120 between abase magnetic portion 122 and a base nonmagnetic portion 123 of a baseportion 12 according to a modification of the above-described preferredembodiment. In the modification illustrated in FIG. 9, each of an edgeportion of the base magnetic portion 122 and an edge portion of the basenonmagnetic portion 123 includes an inclined surface which is inclinedwith respect to the vertical direction. At the boundary portion 120, theinclined surface of the base magnetic portion 122 and the inclinedsurface of the base nonmagnetic portion 123 overlap with each other whenviewed in the vertical direction. An upper surface 31 of the basemagnetic portion 122 is arranged at the same vertical level as that ofan upper surface 33 of the base nonmagnetic portion 123. A lower surface32 of the base magnetic portion 122 is arranged at the same verticallevel as that of a lower surface 34 of the base nonmagnetic portion 123.

In the modification illustrated in FIG. 10, each of an edge portion ofthe base magnetic portion 122 and an edge portion of the basenonmagnetic portion 123 includes a shoulder portion having a thicknesssmaller than that of a neighboring portion thereof. At the boundaryportion 120, the shoulder portion of the base magnetic portion 122 andthe shoulder portion of the base nonmagnetic portion 123 overlap witheach other when viewed in the vertical direction. An upper surface 31 ofthe base magnetic portion 122 is arranged at the same vertical level asthat of an upper surface 33 of the base nonmagnetic portion 123. A lowersurface 32 of the base magnetic portion 122 is arranged at the samevertical level as that of a lower surface 34 of the base nonmagneticportion 123.

When the base magnetic portion 122 and the base nonmagnetic portion 123are arranged to overlap with each other at the boundary portion 120 whenviewed in the vertical direction as illustrated in each of FIGS. 9 and10, an area of contact between the base magnetic portion 122 and thebase nonmagnetic portion 123 at the boundary portion 120 is increased.This allows the base magnetic portion 122 and the base nonmagneticportion 123 to be securely fixed to each other.

As illustrated in FIG. 6, the base magnetic portion 122 further includesthe magnetic outer circumferential portion 124 surrounding the outerperiphery of the base nonmagnetic portion 123. Each of the magneticelement portions 125 is arranged to project radially inward from themagnetic outer circumferential portion 124. The base nonmagnetic portion123 further includes the nonmagnetic central portion 126, to which thelower end of the shaft 15 is fixed. Each of the nonmagnetic elementportions 127 is arranged to project radially outward from thenonmagnetic central portion 126. This structure of the base portion 12allows the magnetic element portions 125 and the nonmagnetic elementportions 127 to be easily defined. This in turn makes it easy tomanufacture the base portion 12.

As described above, in the base magnetic portion 122, the radially innerend portion of each of the magnetic element portions 125 is arrangedopposite to the magnet portion 17 in the vertical direction. Thiscontributes to increasing the cogging torque generated between themagnetic element portion 125 and the magnet portion 17. This makes iteasier to prevent each magnetic pole 171 of the magnet portion 17 frombeing positioned at any dead point when the rotating portion is in thestopped state.

In addition, the circumferential width of the portion of each magneticelement portion 125 which is opposed to the magnet portion 17 in thevertical direction is equal to or smaller than the circumferential widthof each magnetic pole 171 of the magnet portion 17 at any radialposition. This contributes to preventing a magnetic force from actingbetween each magnetic element portion 125 and any magnetic pole 171adjacent to the magnetic pole 171 positioned over the magnetic elementportion 125. This makes it easier to prevent each magnetic pole 171 ofthe magnet portion 17 from being positioned at any dead point when therotating portion is in the stopped state.

Further, the circumferential width of each of the magnetic elementportions 125 is arranged to decrease in the radially inward direction.This makes it easier to define the magnetic element portions 125 whenthe base magnetic portion 122 is manufactured. This in turn makes iteasier to manufacture the base portion 12.

As described above, the coil portion 14 is defined by the single annularcoil 141 inside of which the shaft 15 is arranged. In other words, thevibration motor 1 includes the single coil 141 attached onto the circuitboard 13. In the coil 141, each of the two long side portions 145 is thetorque generating portion which causes the torque to rotate the rotatingportion to be generated between the magnet portion 17 and the coil 141.Thus, the coil portion 14 provides a greater length of the torquegenerating portion than in the case where a plurality of relativelysmall annular coils are arranged around the shaft 15. This contributesto reducing the size of the coil portion 14 while limiting a reductionin vibrations of the vibration motor 1. A reduction in the longitudinaldimension of the coil portion 14 leads to a reduction in the radialdimension of the vibration motor 1.

Each radially outer end portion of the coil 141 is arranged radiallyoutward of the outer circumferential edge of the magnet portion 17. Thiscontributes to increasing the length of each aforementioned torquegenerating portion of the coil 141. This in turn contributes toincreasing the torque to rotate the rotating portion of the vibrationmotor 1.

In addition, because the number of coils 141 included in the coilportion 14 is one, the number of points of connection between thecoil(s) 141 and the circuit board 13 is minimized. This results in areduced number of processes required to manufacture the vibration motor1. Moreover, because only one coil 141 needs to be positioned when thecoil portion 14 is attached onto the circuit board 13, the manufactureof the vibration motor 1 is simplified when compared to the case where aplurality of coils need to be positioned.

As described above, the coil 141 includes the two long side portions 145which extend in the longitudinal direction of the coil 141 and whichhave the shaft 15 arranged therebetween. That is, the torque generatingportions of the coil 141 are arranged at two positions away from eachother in the circumferential direction by about 180 degrees. At the twopositions, the two long side portions 145 of the coil 141 are arrangedin proximity to each other. The number of magnetic poles 171 of themagnet portion 17 is a multiple of two, and this contributes to easilypreventing the circumferential middle of each of the magnetic poles 171from coinciding with any of the aforementioned two positions when viewedin the vertical direction. In other words, each magnetic pole 171 of themagnet portion 17 can be easily prevented from being positioned at anydead point when the rotating portion is in the stopped state. Further,arranging the number of magnetic poles 171 to be a multiple of fourcontributes to more easily preventing each magnetic pole 171 of themagnet portion 17 from being positioned at any dead point when therotating portion is in the stopped state.

In addition, in the magnet portion 17, the magnetic poles 171 arearranged at equal angular intervals in the circumferential direction.This also contributes to easily preventing the circumferential middle ofeach of the magnetic poles 171 from coinciding with any of theaforementioned two positions when viewed in the vertical direction. Inother words, each magnetic pole 171 of the magnet portion 17 can beeasily prevented from being positioned at any dead point when therotating portion is in the stopped state.

As described above, the number of magnetic element portions 125 is equalto or smaller than the number of magnetic poles 171. This contributes toincreasing the probability that the circumferential middle of anymagnetic pole 171 will be positioned over the circumferential middle ofeach magnetic element portion 125 when the rotating portion stops. Thismakes it easier to prevent each magnetic pole 171 of the magnet portionfrom being positioned at any dead point when the rotating portion is inthe stopped state.

In the preferred embodiment illustrated in FIG. 8, the number ofmagnetic element portions 125 is equal to the number of magnetic poles171. In addition, both the magnetic poles 171 and the magnetic elementportions 125 are arranged at equal angular intervals in thecircumferential direction. This contributes to further increasing theprobability that the circumferential middle of any magnetic pole 171will be positioned over the circumferential middle of each magneticelement portion 125 when the rotating portion stops. This makes it stilleasier to prevent each magnetic pole 171 of the magnet portion 17 frombeing positioned at any dead point when the rotating portion is in thestopped state.

In order to easily prevent each magnetic pole 171 from being positionedat any dead point when the rotating portion is in the stopped state, itis preferable that the number of coils 141 be one, the number ofmagnetic poles 171 of the magnet portion 17 be four, and the number ofmagnetic element portions 125 be four, as described above.

As described above, the coil 141 includes the two long side portions 145which extend in the longitudinal direction of the coil 141 and whichhave the shaft 15 arranged therebetween. The width of the interspacebetween the two long side portions 145 is smaller on one side of thelongitudinal middle of the coil 141 than on the other side of thelongitudinal middle. In addition, on the above one side of thelongitudinal middle of the coil 141, the electronic component 24 isattached onto the circuit board 13 at a position close to one of thelong side portions 145 of the coil 141, that is, near the one of thelong side portions 145. This allows the electronic component 24 to bearranged at a position away from an outer edge of the base portion 12.This makes it easy to arrange the electronic component 24 while limitingan increase in the size of the vibration motor 1.

The angle A1 defined between the coil middle plane S5 and the componentmiddle plane S6 is 45 degrees. This makes it easy to arrange theelectronic component 24. In addition, the lead wires 147 extending fromthe coil 141 are connected to the circuit board 13 on the opposite sideof the coil 141 with respect to the electronic component 24. Thisprevents the lead wires 147 extending from the coil 141 from limitingthe arrangement of the electronic component 24. This makes it stilleasier to arrange the electronic component 24.

Note that the shape of the coil 141 does not need to be limited to theabove-described example, but may be modified in various manners. Each ofFIGS. 11 and 12 is a plan view of a stationary portion according to amodification of the above-described preferred embodiment, in which thecoil has a different shape. In the modification illustrated in FIG. 11,a coil 141 a includes two long side portions 145 arranged to extend inthe longitudinal direction of the coil 141 a and to have a shaft 15arranged therebetween. In more detail, each of the two long sideportions 145 is arranged to extend along a coil middle plane S5 but notin parallel with the coil middle plane S5. The width of an interspacebetween the two long side portions 145 is arranged to gradually decreasewith increasing distance from a longitudinal middle of the coil 141 a.In other words, in a plan view, the coil 141 a is substantially in theshape of a rhombus, and is elongated in the longitudinal direction. Anelectronic component 24 is attached onto a circuit board 13 at aposition close to and outside of one of the long side portions 145 ofthe coil 141 a and away from the longitudinal middle of the coil 141 ain the longitudinal direction. This makes it easy to arrange theelectronic component 24 while limiting an increase in the size of avibration motor 1, as is similarly the case with the preferredembodiment illustrated in FIG. 5. When the coil 141 a is provided, aspacer 22 may include, for example, an annular portion arranged oppositeto an upper surface of the coil 141 a in the vertical direction, and acylindrical portion arranged to extend downward from an innercircumferential edge of the annular portion.

In the modification illustrated in FIG. 12, a coil 141 b includes twolong side portions 145 and two short side portions 146. Each of the twolong side portions 145 is arranged to extend in a longitudinal directionof the coil 141 b and to have a shaft 15 arranged therebetween. One ofthe two long side portions 145 includes a recessed portion 148 arrangedto be recessed toward the other long side portion 145 at one positionalong the longitudinal direction. In the modification illustrated inFIG. 12, the recessed portion 148 is defined in the one of the long sideportions 145 at a position away from a longitudinal middle thereof. Inaddition, an outer edge of the recessed portion 148 is defined by twostraight lines. Except at the recessed portion 148, each of the two longside portions 145 is substantially parallel to a coil middle plane S5.An electronic component 24 is attached onto a circuit board 13 at aposition close to the aforementioned one position in the aforementionedone of the long side portions 145. The electronic component 24 isarranged adjacent to the recessed portion 148 of the one of the longside portions 145 and outside of the coil 141 b. This makes it easy toarrange the electronic component 24 while limiting an increase in thesize of a vibration motor 1, as is similarly the case with the preferredembodiment illustrated in FIG. 5.

Note that the outer edge of the recessed portion 148 of the coil 141 bmay alternatively be defined by a curve as illustrated in FIG. 13. Alsonote that the recessed portion 148 may alternatively be defined in thelongitudinal middle of the long side portion 145 as illustrated in eachof FIGS. 14 and 15. In a modification of the above-described preferredembodiment illustrated in FIG. 14, a recessed portion 148 is defined inthe longitudinal middle of one of long side portions 145, and the otherlong side portion 145 is arranged to be substantially parallel to theone of the long side portions 145. In the modification illustrated inFIG. 14, an entire outer edge of the one of the long side portions 145defines the recessed portion 148. In a modification of theabove-described preferred embodiment illustrated in FIG. 15, a recessedportion 148 is defined in the middle of each of two long side portions145. In the modification illustrated in FIG. 15, an entire outer edge ofeach long side portion 145 defines the recessed portion 148.

As illustrated in FIG. 2, the vibration motor 1 includes the spacer 22.The spacer 22 is attached to the shaft 15 between the bearing portion 21and the coil portion 14. The upper surface 223 of the spacer 22 isarranged to be in contact with the lower surface 211 of the bearingportion 21. The lower surface 221 of the spacer 22 is arranged oppositeto the upper surface 142 of the coil portion 14 in the verticaldirection. Thus, in the vibration motor 1, the coil 141 of the coilportion 14 can be arranged radially closer to the shaft 15 than in avibration motor in which a shaft and a spacer are arranged inside of asingle coil, and than in a vibration motor in which a spacer is arrangedradially inside of a plurality of coils arranged around a shaft. Thiscontributes to reducing the radial dimension of the vibration motor 1while limiting a reduction in the vibrations of the vibration motor 1.

As described above, the lower surface 221 of the spacer 22 is arrangedto be in contact with the upper surface 142 of the coil 141 of the coilportion 14. This contributes to reducing the vertical dimension of thevibration motor 1. In addition, if the vibration motor 1 falls, forexample, vertical movement of the coil 141 is limited, and thiscontributes to preventing the coil 141 from being detached from thecircuit board 13. Further, the vertical position of the upper surface142 of the coil 141 can be fixed, and this makes it easy to secure avertical distance between the coil portion 14 and the magnet portion 17,that is, a gap between the coil portion 14 and the magnet portion 17.

As described above, the spacer 22 is attached to the shaft 15 throughpress fitting. This allows the spacer 22 to be securely fixed to theshaft 15. This in turn contributes to more effectively preventing thecoil 141 of the coil portion 14 from being detached from the circuitboard 13 if the vibration motor 1 falls, for example. In addition, thismakes it easier to secure the vertical distance between the coil portion14 and the magnet portion 17.

In the vibration motor 1, the spacer 22 is in the shape of a circularring or in the shape of the letter “C”, and is made of the resin. Thisallows the spacer 22 to have a simple shape. This in turn allows thespacer 22 to be easily manufactured.

As described above, the lower end of the shaft 15 is fixed in the basecentral through hole 128, which passes through the base portion 12 inthe vertical direction. This contributes to reducing the thickness ofthe base portion 12, and reducing the thickness of the vibration motor1. In addition, this makes it possible to securely fix the shaft 15 tothe base portion 12.

In the vibration motor 1, the upper surface of the entire portion of thebase portion 12 which lies between the shaft 15 and the innercircumferential edge of the coil 141 in the plan view is arranged at thesame vertical level. This contributes to further reducing the thicknessof the base portion 12. In addition, this contributes to simplifying theformation of the base portion 12. Further, absence of a protrusionaround the shaft 15 in the base portion 12 allows the coil portion 14 tobe arranged closer to the shaft 15. This contributes to reducing theradial dimension of the vibration motor 1. In addition, the length ofeach torque generating portion of the coil 141 can thus be increased,and this contributes to increasing the vibrations of the vibration motor1.

Moreover, the upper surface of the entire portion of the base portion 12which lies between the shaft 15 and the magnetic element portions 125and the nonmagnetic element portions 127 is arranged at the samevertical level. This contributes to further reducing the thickness ofthe base portion 12, as in the case where the upper surface of theentire portion of the base portion 12 which lies between the shaft 15and the inner circumferential edge of the coil 141 in the plan view isarranged at the same vertical level. In addition, this contributes tosimplifying the formation of the base portion 12. Further, absence of aprotrusion around the shaft 15 in the base portion 12 allows the coilportion 14 to be arranged closer to the shaft 15. This contributes toreducing the radial dimension of the vibration motor 1. In addition, thelength of each torque generating portion of the coil 141 can thus beincreased, and this contributes to increasing the vibrations of thevibration motor 1.

FIG. 16 is a plan view illustrating a base portion 12 a according to amodification of the above-described preferred embodiment. The baseportion 12 a illustrated in FIG. 16 includes a base magnetic portion 122and a base nonmagnetic portion 123. The base portion 12 a is differentfrom the base portion 12 illustrated in FIG. 6 in the shape of the basemagnetic portion 122 and the shape of the base nonmagnetic portion 123.As illustrated in FIG. 16, the base nonmagnetic portion 123 of the baseportion 12 a includes a nonmagnetic outer circumferential portion 126 aand a plurality of nonmagnetic element portions 127. In the modificationillustrated in FIG. 16, the base nonmagnetic portion 123 includes fournonmagnetic element portions 127. The nonmagnetic outer circumferentialportion 126 a is substantially annular. In more detail, the nonmagneticouter circumferential portion 126 a is substantially in the shape of acircular ring, and is centered on a central axis J1. The nonmagneticouter circumferential portion 126 a is arranged to surround an outerperiphery of the base magnetic portion 122.

Each of the nonmagnetic element portions 127 is defined integrally withthe nonmagnetic outer circumferential portion 126 a. Each of thenonmagnetic element portions 127 is arranged to project radially inwardfrom the nonmagnetic outer circumferential portion 126 a. Eachnonmagnetic element portion 127 is a nonmagnetic projecting portionarranged to project from an inner circumferential edge of thenonmagnetic outer circumferential portion 126 a substantiallyperpendicularly to the vertical direction toward the central axis J1.Each of the nonmagnetic element portions 127 is arranged to have thesame shape. The circumferential width of each of the nonmagnetic elementportions 127 is arranged to decrease in the radially inward direction.

The base magnetic portion 122 of the base portion 12 a includes amagnetic central portion 124 a and a plurality of magnetic elementportions 125. In the modification illustrated in FIG. 16, the basemagnetic portion 122 includes four magnetic element portions 125. Themagnetic central portion 124 a is substantially in the shape of a disk,and is centered on the central axis J1. A base central through hole 128,which passes through the base portion 12 a in the vertical direction, isdefined in a central portion of the magnetic central portion 124 a.

Each of the magnetic element portions 125 is defined integrally with themagnetic central portion 124 a. Each of the magnetic element portions125 is arranged to project radially outward from the magnetic centralportion 124 a. Each magnetic element portion 125 is a magneticprojecting portion arranged to project from an outer circumferentialedge of the magnetic central portion 124 a substantially perpendicularlyto the vertical direction. Each of the magnetic element portions 125 isarranged to have the same shape. The magnetic element portions 125 arearranged to extend from the magnetic central portion 124 a in a radialmanner with the central axis J1 as a center. The circumferential widthof each of the magnetic element portions 125 is arranged to decrease inthe radially outward direction.

The nonmagnetic element portions 127 are arranged to alternate with themagnetic element portions 125 in the circumferential direction. Thecircumferential width of each magnetic element portion 125 is smallerthan the circumferential width of each nonmagnetic element portion 127at any radial position. The magnetic element portions 125 and thenonmagnetic element portions 127 are arranged in the circumferentialdirection, and are arranged at positions opposed to a magnet portion 17in the vertical direction. The magnetic element portions 125 arearranged at equal angular intervals in the circumferential direction.The nonmagnetic element portions 127 are also arranged at equal angularintervals in the circumferential direction.

Similarly to the base portion 12, the base portion 12 a is made of ametal. This contributes to reducing the thickness of the base portion 12a while limiting a reduction in strength of the base portion 12 a.

In the base portion 12 a, as in the base portion 12, the basenonmagnetic portion 123 is fixed to an edge portion of the base magneticportion 122, and is arranged to extend from the edge portion of the basemagnetic portion 122 perpendicularly to the vertical direction. The basemagnetic portion 122 includes the magnetic element portions 125 asdescribed above. The magnetic element portions 125 are arranged in thecircumferential direction, and are arranged at the positions opposed tothe magnet portion 17 in the vertical direction. The base nonmagneticportion 123 includes the nonmagnetic element portions 127. Thenonmagnetic element portions 127 are arranged to alternate with themagnetic element portions 125 in the circumferential direction, and arearranged at the positions opposed to the magnet portion 17 in thevertical direction. In a vibration motor 1 including the base portion 12a, as in the vibration motor 1 including the base portion 12, each ofmagnetic poles 171 of the magnet portion 17 can be prevented from beingpositioned at any dead point when a rotating portion is in the stoppedstate.

In the base portion 12 a, as in the base portion 12, the base magneticportion 122 and the base nonmagnetic portion 123 do not overlap witheach other at any position outside of a boundary portion between thebase magnetic portion 122 and the base nonmagnetic portion 123 whenviewed in the vertical direction. This contributes to reducing thethickness of the base portion 12 a. This in turn leads to a reducedthickness of the vibration motor 1.

In addition, in the base portion 12 a, the base magnetic portion 122 andthe base nonmagnetic portion 123 do not overlap with each other even atthe boundary portion 120 when viewed in the vertical direction. Thiscontributes to a further reduction in the thickness of the base portion12 a. This in turn leads to a further reduction in the thickness of thevibration motor 1. Moreover, the edge portion of the base magneticportion 122 and an edge portion of the base nonmagnetic portion 123 canbe easily defined. This makes it easy to manufacture the base portion 12a.

As described above, the base nonmagnetic portion 123 further includesthe nonmagnetic outer circumferential portion 126 a surrounding theouter periphery of the base magnetic portion 122. Each of thenonmagnetic element portions 127 is arranged to project radially inwardfrom the nonmagnetic outer circumferential portion 126 a. The basemagnetic portion 122 further includes the magnetic central portion 124a, to which a lower end of a shaft 15 is fixed. Each of the magneticelement portions 125 is arranged to project radially outward from themagnetic central portion 124 a. This structure of the base portion 12 aallows the magnetic element portions 125 and the nonmagnetic elementportions 127 to be easily defined. This makes it easy to manufacture thebase portion 12 a.

In the base magnetic portion 122, a radially outer end portion of eachof the magnetic element portions 125 is arranged opposite to the magnetportion 17 in the vertical direction. This contributes to increasingcogging torque generated between the magnetic element portion 125 andthe magnet portion 17. This makes it easier to prevent each magneticpole 171 of the magnet portion from being positioned at any dead pointwhen the rotating portion is in the stopped state.

In addition, the circumferential width of a portion of each magneticelement portion 125 which is opposed to the magnet portion 17 in thevertical direction is equal to or smaller than the circumferential widthof each magnetic pole 171 of the magnet portion 17 at any radialposition. This contributes to preventing a magnetic force from actingbetween each magnetic element portion 125 and any magnetic pole 171adjacent to the magnetic pole 171 positioned over the magnetic elementportion 125. This makes it easier to prevent each magnetic pole 171 ofthe magnet portion 17 from being positioned at any dead point when therotating portion is in the stopped state.

Further, the circumferential width of each of the magnetic elementportions 125 is arranged to decrease in the radially outward direction.This makes it easy to define the magnetic element portions 125 when thebase magnetic portion 122 is manufactured. This in turn makes it easy tomanufacture the base portion 12 a.

The base portion 12 a includes a base peripheral through hole 129, whichpasses through the base portion 12 a in the vertical direction, at aposition away from the shaft 15. In the modification illustrated in FIG.16, the base peripheral through hole 129 is defined in the base magneticportion 122, the outer periphery of which is surrounded by the basenonmagnetic portion 123. The base peripheral through hole 129 is thusdefined at a position away from an outer edge portion of the baseportion 12 a, and this contributes to limiting a reduction in thestrength of the base portion 12 a caused by the base peripheral throughhole 129.

As described above, in each of the base portions 12 and 12 a, one of thebase nonmagnetic portion 123 and the base magnetic portion 122 isarranged to surround the outer periphery of the other one of the basenonmagnetic portion 123 and the base magnetic portion 122. Then, thebase peripheral through hole 129 is defined in the other one of the basenonmagnetic portion 123 and the base magnetic portion 122. The baseperipheral through hole 129 is thus defined at a position away from theouter edge portion of the base portion 12 or 12 a, and this contributesto limiting a reduction in the strength of the base portion 12 or 12 acaused by the base peripheral through hole 129.

FIG. 17 is a plan view illustrating a base portion 12 b according toanother modification of the above-described preferred embodiment. InFIG. 17, as in FIG. 8, a magnet portion 17, a coil portion 14, and thebase portion 12 b are shown. The base portion 12 b illustrated in FIG.17 is different from the base portion 12 illustrated in FIG. 6 incircumferential positions of a plurality of magnetic element portions125 and a plurality of nonmagnetic element portions 127. In addition, inFIG. 17, the orientation of the coil portion 14 is different from thatin FIG. 8.

In FIG. 17, as in FIG. 6, a first plane S1, which includes a centralaxis J1 and a circumferential middle of a base projecting portion 121,is represented by a chain double-dashed line. A coil middle plane S5,which is parallel to a longitudinal direction of a coil 141 and whichincludes the central axis J1, coincides with the first plane S1. Inaddition, a second plane S2, which includes the central axis J1 and acircumferential middle of one of the magnetic element portions 125 thatis closest to the first plane S1 in the circumferential direction of allthe magnetic element portions 125, is also represented by a chaindouble-dashed line. In FIG. 17, the magnetic element portion 125 in theupper left of the figure is regarded as this one of the magnetic elementportions 125. An angle A3 defined between the first plane S1 and thesecond plane S2 is, for example, 22.5 degrees. The angle A3 is equal to90 degrees divided by the number of magnetic poles 171. This contributesto more easily preventing each magnetic pole 171 of the magnet portion17 from being positioned at any dead point when a rotating portion is inthe stopped state.

FIG. 18 is a vertical sectional view of a vibration motor 1 a accordingto a second preferred embodiment of the present invention. FIG. 19 is aperspective view illustrating a rotating portion and a stationaryportion of the vibration motor 1 a. The vibration motor 1 a includes therotating portion and a spacer 22 a, which are different in shape fromthe rotating portion and the spacer 22, respectively, of the vibrationmotor 1 illustrated in FIG. 2. The rotating portion of the vibrationmotor 1 a includes a bearing portion 21 a, a rotor holder 16 a, a magnetportion 17, and an eccentric weight 18 a. The vibration motor 1 a isotherwise similar in structure to the vibration motor 1 illustrated inFIGS. 1 to 6, and accordingly, like members or portions are designatedby like reference numerals.

The spacer 22 a is a substantially annular, tubular member including athrough hole defined in a center thereof. In the preferred embodimentillustrated in FIG. 18, the spacer 22 a is in the shape of a circularring, and is centered on a central axis J1. Note that the spacer 22 amay alternatively be, for example, in the shape of the letter “C”, thatis, a circular ring with one circumferential portion omitted. A shaft 15is inserted through the through hole of the spacer 22 a. The spacer 22 ais attached to the shaft 15 through, for example, press fitting. Thespacer 22 a is arranged above a coil portion 14, and is fixed to theshaft 15. The spacer 22 a is made of, for example, a resin. Note thatthe spacer 22 a may alternatively be made of another material. Also notethat the spacer 22 a may alternatively be attached to the shaft 15 by amethod other than press fitting.

A lower surface 221 of the spacer 22 a is arranged opposite to an uppersurface 142 of a coil 141 of the coil portion in the vertical direction.In the preferred embodiment illustrated in FIG. 18, the lower surface221 of the spacer 22 a is arranged to be in contact with the uppersurface 142 of the coil 141 of the coil portion 14. The spacer 22 a isarranged radially inside of the magnet portion 17. In other words, anupper surface 223 of the spacer 22 a is arranged at a level higher thanthat of a lower surface of the magnet portion 17. This contributes toreducing the vertical dimension of the vibration motor 1 a when comparedto a vibration motor in which a magnet portion is arranged above anupper surface of a spacer. The spacer 22 a is arranged radially oppositeto the magnet portion 17 with a gap therebetween.

The bearing portion 21 a is an annular member including a through holedefined in a center thereof. In the preferred embodiment illustrated inFIG. 18, the bearing portion 21 a is substantially cylindrical, and iscentered on the central axis J1. The shaft 15 is inserted through thethrough hole of the bearing portion 21 a. The bearing portion 21 a isattached to the shaft 15 to be rotatable with respect to the shaft 15above the coil 141 of the coil portion 14. In addition, the bearingportion 21 a is arranged above the spacer 22 a. In other words, thespacer 22 a is attached to the shaft 15 between the bearing portion 21 aand the coil 141 of the coil portion 14. The upper surface 223 of thespacer 22 a is arranged to be in contact with a lower surface 211 of thebearing portion 21 a.

The rotor holder 16 a is a member substantially in the shape of acircular ring. The rotor holder 16 a is attached to the bearing portion21 a. In more detail, an inner circumferential portion of the rotorholder 16 a, which is substantially in the shape of an annular plate, isfixed to an upper end surface and an upper portion of an outercircumferential surface of the bearing portion 21 a. The rotor holder 16a is thus supported by the bearing portion 21 a to be rotatable withrespect to the shaft 15. The rotor holder 16 a is made of, for example,a metal.

The magnet portion 17 is a member substantially in the shape of acircular ring, and is centered on the central axis J1. The magnetportion 17 is attached to the rotor holder 16 a. In more detail, anupper surface of the magnet portion 17, which is substantiallycylindrical, is attached to a lower surface of the rotor holder 16 a.The magnet portion 17 is arranged above the coil 141 of the coil portion14, and is arranged opposite to the coil 141 in the vertical directionwith a gap therebetween. The magnet portion 17 is arranged around thebearing portion 21 a and the spacer 22 a. The bearing portion 21 a isarranged radially inside of the magnet portion 17, and is arrangedradially opposite to the magnet portion 17 with a gap therebetween.

The eccentric weight 18 a is arranged to have a shape corresponding tothat of a left half of a member substantially in the shape of a coveredcylinder. The eccentric weight 18 a is substantially in the shape of asemicircle in a plan view. The eccentric weight 18 a is attached to therotor holder 16 a. In more detail, a lower surface of a top coverportion 181 of the eccentric weight 18 a is attached to an upper surfaceof the rotor holder 16 a through, for example, an adhesive. A side wallportion 182 of the eccentric weight 18 a is arranged to cover a portionof a lateral side of the rotor holder 16 a and a portion of a lateralside of the magnet portion 17. A lower end of the side wall portion 182of the eccentric weight 18 a is arranged at substantially the samevertical level as that of a lower end of the magnet portion 17. Thecenter of gravity of the eccentric weight 18 a is radially away from thecentral axis J1.

The vibration motor 1 a includes the base portion 12 illustrated in FIG.6. As described above, the base portion 12 includes the base magneticportion 122 and the base nonmagnetic portion 123. The base magneticportion 122 and the base nonmagnetic portion 123 do not overlap witheach other at any position outside of the boundary portion between thebase magnetic portion 122 and the base nonmagnetic portion 123 whenviewed in the vertical direction. This allows the base portion 12 tohave a smaller thickness than in the case where the base magneticportion 122 and the base nonmagnetic portion 123 overlap with each otherat a position other than the boundary portion 120. This leads to areduced thickness of the vibration motor 1 a.

The vibration motor 1 a includes the coil portion 14 illustrated in FIG.5. As described above, the coil portion 14 is defined by the singleannular coil 141 inside of which the shaft 15 is arranged. In the coil141, each of the two long side portions 145 is the torque generatingportion which causes a torque to rotate the rotating portion to begenerated between the magnet portion 17 and the coil 141. This makes itpossible to reduce the size of the coil portion 14 while limiting areduction in vibrations of the vibration motor 1 a. A reduction in thelongitudinal dimension of the coil portion 14 leads to a reduction inthe radial dimension of the vibration motor 1 a.

FIG. 20 is a vertical sectional view of a vibration motor 1 b accordingto a third preferred embodiment of the present invention. The vibrationmotor 1 b includes a rotor holder 16 b and a spacer 22 b, which aredifferent in shape from the rotor holder 16 a and the spacer 22 a,respectively, of the vibration motor 1 a illustrated in FIGS. 18 and 19.The vibration motor 1 b is otherwise similar in structure to thevibration motor 1 a illustrated in FIGS. 18 and 19, and accordingly,like members or portions are designated by like reference numerals.

The spacer 22 b is a substantially annular, tubular member including athrough hole defined in a center thereof. In the preferred embodimentillustrated in FIG. 20, the spacer 22 b is in the shape of a circularring, and is centered on a central axis J1. Note that the spacer 22 bmay alternatively be, for example, in the shape of the letter “C”, thatis, a circular ring with one circumferential portion omitted. A shaft 15is inserted through the through hole of the spacer 22 b. The spacer 22 bis attached to the shaft 15 through, for example, press fitting. Thespacer 22 b is arranged above a coil portion 14, and is fixed to theshaft 15. The spacer 22 b is made of, for example, a resin. Note thatthe spacer 22 b may alternatively be made of another material. Also notethat the spacer 22 b may alternatively be attached to the shaft 15 by amethod other than press fitting.

A lower surface 221 of the spacer 22 b is arranged opposite to an uppersurface 142 of a coil 141 of the coil portion 14 in the verticaldirection. In the preferred embodiment illustrated in FIG. 20, the lowersurface 221 of the spacer 22 b is arranged to be in contact with theupper surface 142 of the coil 141 of the coil portion 14. The spacer 22b is arranged radially inside of a magnet portion 17. In other words, anupper surface 223 of the spacer 22 b is arranged at a level higher thanthat of a lower surface of the magnet portion 17. This contributes toreducing the vertical dimension of the vibration motor 1 b when comparedto a vibration motor in which a magnet portion is arranged above anupper surface of a spacer. The spacer 22 b is arranged radially oppositeto the magnet portion 17 with a gap therebetween.

The rotor holder 16 b is attached to a bearing portion 21 b. In moredetail, an inner circumferential portion 161 of the rotor holder 16 b isattached to an upper end surface and an outer circumferential surface ofthe bearing portion 21 b. The inner circumferential portion 161 of therotor holder 16 b is fixed to the substantially entire outercircumferential surface of the bearing portion 21 b. This allows therotor holder 16 b to be securely attached to the bearing portion 21 b.The rotor holder 16 b is bent radially outward and upward at a lower endportion of the inner circumferential portion 161, and is then bentradially outward to extend radially outward.

In the vibration motor 1 b, a top cover portion of a cover portion 11includes a cover projecting portion 111 at a junction of the top coverportion with the shaft 15. The cover projecting portion 111 is arrangedto project downward along the shaft 15. This increases the verticaldimension of an area over which the cover portion 11 and the shaft 15are joined to each other. This allows the cover portion 11 to be moresecurely fixed to the shaft 15.

Similarly to the vibration motor 1 a, the vibration motor 1 b includesthe base portion 12 illustrated in FIG. 6. This contributes to reducingthe thickness of the base portion 12, and, in turn, contributes toreducing the thickness of the vibration motor 1 b. In addition,similarly to the vibration motor 1 a, the vibration motor 1 b includesthe coil portion 14 including the coil 141 illustrated in FIG. 5. Thisallows the longitudinal dimension of the coil portion 14 to be reducedto reduce the radial dimension of the vibration motor 1 b, whilelimiting a reduction in vibrations of the vibration motor 1 b.

FIG. 21 is a vertical sectional view of a vibration motor 1 c accordingto a fourth preferred embodiment of the present invention. FIG. 22 is aperspective view illustrating a rotating portion and a stationaryportion of the vibration motor 1 c. The orientation of an eccentricweight 18 in FIGS. 21 and 22 is different from the orientation of theeccentric weight 18 a in FIGS. 18 and 19 by 90 degrees. The vibrationmotor 1 c includes a rotor holder 16 c, a bearing portion 21 c, and aspacer 22 c, which are different in shape from the rotor holder 16 a,the bearing portion 21 a, and the spacer 22 a, respectively, of thevibration motor 1 a illustrated in FIGS. 18 and 19. The vibration motor1 c is otherwise similar in structure to the vibration motor 1 aillustrated in FIGS. 18 and 19, and accordingly, like members orportions are designated by like reference numerals.

The spacer 22 c is arranged to have the same shape as that of the spacer22 illustrated in FIG. 2, and is made of the same material as that ofthe spacer 22, for example. Similarly to the spacer 22, the spacer 22 cis attached to the shaft 15, for example. A lower surface 221 of thespacer 22 c is arranged opposite to an upper surface 142 of a coil 141of a coil portion in the vertical direction. In the preferred embodimentillustrated in FIGS. 21 and 22, the lower surface 221 of the spacer 22 cis arranged to be in contact with the upper surface 142 of the coil 141of the coil portion 14.

The rotor holder 16 c is substantially in the shape of an annular plate,and is centered on a central axis J1. The bearing portion 21 c is, forexample, made of a resin, and is defined integrally with the rotorholder 16 c and the eccentric weight 18 by an insert molding process. Alarge part of the rotating portion is thus defined by the insert moldingprocess, and this contributes to reducing the number of parts of thevibration motor 1 c. This leads to simpler assemblage of the vibrationmotor 1 c.

Similarly to the vibration motor 1 a, the vibration motor 1 c includesthe base portion 12 illustrated in FIG. 6. This contributes to reducingthe thickness of the base portion 12, and, in turn, contributes toreducing the thickness of the vibration motor 1 c. In addition,similarly to the vibration motor 1 a, the vibration motor 1 c includesthe coil portion 14 including the coil 141 illustrated in FIG. 5. Thisallows the longitudinal dimension of the coil portion 14 to be reducedto reduce the radial dimension of the vibration motor 1 c, whilelimiting a reduction in vibrations of the vibration motor 1 c.

In each of the vibration motors 1 a, 1 b, and 1 c, the above-describedbase portion 12 a or the above-described base portion 12 b may be usedin place of the base portion 12. Even in this case, each of thevibration motors 1 a, 1 b, and 1 c is able to achieve a reducedthickness as described above. In each of the vibration motors 1 a, 1 b,and 1 c, the coil 141 a or the coil 141 b may be used in place of thecoil 141. Even in this case, each of the vibration motors 1 a, 1 b, and1 c is able to achieve a reduced radial dimension.

FIG. 23 is a perspective view illustrating a stationary portion of avibration motor 1 d according to a fifth preferred embodiment of thepresent invention. FIG. 24 is a plan view of the stationary portion ofthe vibration motor 1 d. FIG. 25 is a plan view of a base portion 12 dof the vibration motor 1 d. FIG. 26 is a plan view illustrating a magnetportion 17 d, a coil portion 14 d, and the base portion 12 d. FIG. 26 isa diagram illustrating an example stop position of the magnet portion 17d. The vibration motor 1 d includes the magnet portion 17 d, the coilportion 14 d, the base portion 12 d, and a spacer 22 d, which aredifferent in shape from the magnet portion 17, the coil portion 14, thebase portion 12, and the spacer 22, respectively, of the vibration motor1 illustrated in FIGS. 1 to 6. The vibration motor 1 d is otherwisesimilar in structure to the vibration motor 1 illustrated in FIGS. 1 to6, and accordingly, like members or portions are designated by likereference numerals.

In the vibration motor 1 d illustrated in FIGS. 23 to 26, the magnetportion 17 d includes a plurality of magnetic poles 171. The number ofmagnetic poles 171 is, for example, a multiple of two. In the preferredembodiment illustrated in FIG. 26, the number of magnetic poles 171 issix. That is, the magnet portion 17 d includes three north poles andthree south poles. The three north poles and the three south poles arearranged to alternate with each other in the circumferential direction.The magnetic poles 171 are arranged at equal angular intervals in thecircumferential direction. In the preferred embodiment illustrated inFIG. 26, the six magnetic poles 171 are arranged at intervals of 60degrees. In other words, in a plan view, an angle defined between astraight line that joins a circumferential middle of each magnetic pole171 and a central axis J1, and a straight line that joins acircumferential middle of the magnetic pole 171 adjacent thereto and thecentral axis J1, is 60 degrees.

The coil portion 14 d is arranged radially opposite to a shaft 15 with agap therebetween. The coil portion 14 d includes at least one coil 141 darranged around the shaft 15. The number of the at least one coil 141 dis equal to or smaller than the number of magnetic poles 171 of themagnet portion 17 d. In the preferred embodiment illustrated in FIG. 23,the at least one coil 141 d is two in number. The two coils 141 d arearranged on opposite sides of the shaft 15. Note that the number ofcoils 141 d included in the coil portion 14 d may alternatively be morethan two. Each coil 141 d is fixed onto a circuit board 13 through anadhesive, for example. In the preferred embodiment illustrated in FIG.24, in a plan view, each coil 141 d is annular, and is arranged tosurround an axis parallel to the shaft 15, with the shaft 15 arrangedoutside of the coil 141 d.

The spacer 22 d is attached to the shaft 15. A lower surface 221 of thespacer 22 d is arranged opposite to an upper surface of the coil portion14 d in the vertical direction. In the preferred embodiment illustratedin FIG. 23, the lower surface 221 of the spacer 22 d is arranged to bein contact with the upper surface of the coil portion 14 d. In moredetail, the lower surface 221 of the spacer 22 d is arranged to be incontact with an upper surface 142 of each of the two coils 141 d of thecoil portion 14 d. As illustrated in FIGS. 23 and 24, an entire innercircumferential edge 143 of the upper surface 142 of each coil 141 d isarranged radially outside of an outer edge 222 of the lower surface 221of the spacer 22 d. In addition, a portion of an outer circumferentialedge 144 of the upper surface 142 of each coil 141 d is arrangedradially inside of the outer edge 222 of the lower surface 221 of thespacer 22 d. In other words, the lower surface 221 of the spacer 22 dlies over a portion of the upper surface 142 of each coil 141 d, butdoes not lie over an opening defined in a central portion of the uppersurface 142.

Similarly to the base portion 12 illustrated in FIG. 6, the base portion12 d includes a base magnetic portion 122 and a base nonmagnetic portion123. The base nonmagnetic portion 123 is fixed to an edge portion of thebase magnetic portion 122, and is arranged to extend from the edgeportion of the base magnetic portion 122 substantially perpendicularlyto the vertical direction. The base magnetic portion 122 includes amagnetic outer circumferential portion 124 and a plurality of magneticelement portions 125. The base nonmagnetic portion 123 includes anonmagnetic central portion 126 and a plurality of nonmagnetic elementportions 127.

The magnetic outer circumferential portion 124 is arranged to surroundan outer periphery of the base nonmagnetic portion 123. Each of themagnetic element portions 125 is defined integrally with the magneticouter circumferential portion 124. Each of the magnetic element portions125 is arranged to project radially inward from the magnetic outercircumferential portion 124. The circumferential width of each of themagnetic element portions 125 is arranged to decrease in the radiallyinward direction. The magnetic element portions 125 are arranged in thecircumferential direction, and are arranged at positions opposed to themagnet portion 17 d in the vertical direction. The magnetic elementportions 125 are arranged at equal angular intervals in thecircumferential direction. In the preferred embodiment illustrated inFIG. 25, the number of magnetic element portions 125 is three, and thethree magnetic element portions 125 are arranged at intervals of 120degrees.

A base central through hole 128, which passes through the base portion12 d in the vertical direction, is defined in a central portion of thenonmagnetic central portion 126. Each of the nonmagnetic elementportions 127 is defined integrally with the nonmagnetic central portion126. Each of the nonmagnetic element portions 127 is arranged to projectradially outward from the nonmagnetic central portion 126. Thecircumferential width of each of the nonmagnetic element portions 127 isarranged to increase in the radially outward direction. The nonmagneticelement portions 127 are arranged in the circumferential direction, andare arranged at positions opposed to the magnet portion 17 d in thevertical direction. The nonmagnetic element portions 127 are arranged atequal angular intervals in the circumferential direction. In thepreferred embodiment illustrated in FIG. 25, the number of nonmagneticelement portions 127 is three, and the three nonmagnetic elementportions 127 are arranged at intervals of 120 degrees.

A first plane S1 is an imaginary plane including the central axis J1 anda circumferential middle of a base projecting portion 121. A secondplane S2 is an imaginary plane including the central axis J1 and acircumferential middle of one of the magnetic element portions 125 thatis closest to the first plane S1 in the circumferential direction of allthe magnetic element portions 125. An angle A3 defined between the firstplane S1 and the second plane S2 is, for example, 15 degrees. The angleA3 is equal to 90 degrees divided by the number of magnetic poles 171.

The number of magnetic element portions 125 of the base portion 12 d ispreferably equal to or smaller than the number of magnetic poles 171. Inthe preferred embodiment illustrated in FIG. 26, the number of magneticelement portions 125 is equal to a half of the number of magnetic poles171. In FIG. 26, a coil middle plane S4, which is an imaginary planeincluding the central axis J1 and a circumferential middle of each coil141 d, is represented by a chain double-dashed line.

In the vibration motor 1 d, as in the vibration motor 1 described above,the base magnetic portion 122 and the base nonmagnetic portion 123 donot overlap with each other at any position outside of a boundaryportion between the base magnetic portion 122 and the base nonmagneticportion 123 when viewed in the vertical direction. This allows the baseportion 12 d to have a smaller thickness than in the case where the basemagnetic portion 122 and the base nonmagnetic portion 123 overlap witheach other at a position other than the boundary portion 120. This leadsto a reduced thickness of the vibration motor 1 d.

In the base portion 12 d, as in the base portion 12 illustrated in FIG.7, the base magnetic portion 122 and the base nonmagnetic portion 123 donot overlap with each other even at the boundary portion 120 when viewedin the vertical direction. This contributes to a further reduction inthe thickness of the base portion 12 d. This in turn leads to a furtherreduction in the thickness of the vibration motor 1 d. In addition, eachof a side surface of the edge portion of the base magnetic portion 122and a side surface of an edge portion of the base nonmagnetic portion123 is arranged to be substantially parallel to the vertical direction,and this makes it easier to define the edge portion of the base magneticportion 122 and the edge portion of the base nonmagnetic portion 123.This makes it easier to manufacture the base portion 12 d.

Over an area where an upper surface of the base portion 12 d is coveredwith the circuit board 13, an upper surface 31 of the base magneticportion 122 and an upper surface 33 of the base nonmagnetic portion 123are arranged at the same vertical level. This allows the circuit board13 to be securely fixed to the upper surface of the base portion 12 d.In addition, a lower surface of the base magnetic portion 122 and alower surface of the base nonmagnetic portion 123 are also arranged atthe same vertical level. This prevents a projecting portion from beingdefined in the lower surface of the base portion 12 d. This contributesto a further reduction in the thickness of the base portion 12 d. Thisin turn leads to a further reduction in the thickness of the vibrationmotor 1 d.

In the vibration motor 1 d, the base magnetic portion 122 and the basenonmagnetic portion 123 may be arranged to overlap with each other atthe boundary portion 120 when viewed in the vertical direction, asillustrated in FIGS. 9 and 10. When the base magnetic portion 122 andthe base nonmagnetic portion 123 are arranged to overlap with each otherat the boundary portion 120 when viewed in the vertical direction, anarea of contact between the base magnetic portion 122 and the basenonmagnetic portion 123 at the boundary portion 120 is increased. Thisallows the base magnetic portion 122 and the base nonmagnetic portion123 to be securely fixed to each other.

In the vibration motor 1 d, once supply of an electric current to thecoil 141 d of the coil portion 14 d is stopped, cogging torque generatedbetween the magnetic element portions 125 of the base magnetic portion122 and the magnet portion 17 d causes the rotating portion to stopwith, of the magnetic poles 171 of the magnet portion 17 d, the threenorth poles or the three south poles positioned over the three magneticelement portions 125, respectively. In FIG. 26, each of the three northpoles is positioned over a separate one of the three magnetic elementportions 125. In more detail, the rotating portion is caused to stopwith the circumferential middle of each north pole of the magnet portion17 d positioned opposite to the circumferential middle of a separate oneof the magnetic element portions 125 in the vertical direction.

In the preferred embodiment illustrated in FIG. 26, each of the at leastone coil 141 d mentioned above is arranged to be circumferentiallydisplaced from one of the magnetic poles 171 (hereinafter, this magneticpole 171 will be referred to as a “reference magnetic pole”) by an“angle equal to 2M−1 times an angle obtained by dividing 90 degrees bythe number of magnetic poles 171”. Here, M is a natural number equal toor smaller than twice the number of magnetic poles. Because the numberof magnetic poles 171 is six, each coil 141 d is arranged at a positioncircumferentially displaced from the reference magnetic pole by “15degrees×(2M−1)”.

For example, if the north pole at the bottom in FIG. 26 is regarded asthe reference magnetic pole, the coil 141 d on the lower side in FIG. 26is arranged at a position circumferentially, in a clockwise direction,displaced from the reference magnetic pole by 15 degrees. In otherwords, an angle A4 defined between the coil middle plane S4, which isthe imaginary plane including the central axis J1 and thecircumferential middle of this coil 141 d, and a third plane S3, whichis an imaginary plane including the circumferential middle of thereference magnetic pole and the central axis J1, is 15 degrees, which isonce 15 degrees. Meanwhile, the coil 141 d on the upper side in FIG. 26is arranged at a position circumferentially, in the clockwise direction,displaced from the reference magnetic pole by 195 degrees. In otherwords, an angle defined between an imaginary plane including thecircumferential middle of this coil 141 d and the central axis J1 andthe aforementioned third plane S3 is 195 degrees, which is 13 times 15degrees.

As described above, in the vibration motor 1 d, the magnetic poles 171are arranged at intervals of 60 degrees. Accordingly, thecircumferential middle of the magnetic pole 171 that is closest to eachcoil 141 d in the circumferential direction is circumferentiallydisplaced from the circumferential middle of the coil 141 d by 15degrees. Each magnetic pole 171 is thus prevented from being positionedat any dead point, which would prohibit the rotating portion fromstarting rotating, when the rotating portion is in the stopped state.

As described above, in the vibration motor 1 d, the coil portion 14 dincludes the at least one coil 141 d arranged around the shaft 15, andthe number of the at least one coil 141 d is equal to or smaller thanthe number of magnetic poles 171 of the magnet portion 17 d. Thiscontributes to preventing the circumferential middle of each coil 141 dfrom coinciding with the circumferential middle of any magnetic pole 171when viewed in the vertical direction. This makes it easier to preventeach magnetic pole 171 of the magnet portion 17 d from being positionedat any dead point when the rotating portion is in the stopped state.

In order to easily prevent each magnetic pole 171 from being positionedat any dead point when the rotating portion is in the stopped state, itis preferable that the number of coils 141 d be two, the number ofmagnetic poles 171 of the magnet portion 17 d be six, and the number ofmagnetic element portions 125 be three, as described above.

As described above, each of the at least one coil 141 d is arranged tobe circumferentially displaced from one of the magnetic poles 171 by an“angle equal to 2M−1 times an angle obtained by dividing 90 degrees bythe number of magnetic poles 171”. This contributes to preventing thecircumferential middle of each coil 141 d from coinciding with thecircumferential middle of any magnetic pole 171 when viewed in thevertical direction. This makes it still easier to prevent each magneticpole 171 of the magnet portion 17 d from being positioned at any deadpoint when the rotating portion is in the stopped state.

The number of magnetic poles 171 of the magnet portion 17 d is amultiple of two, and this contributes to easily preventing thecircumferential middle of each of the magnetic poles 171 from coincidingwith the circumferential middle of any of the two coils 141 d whenviewed in the vertical direction. In other words, each magnetic pole 171of the magnet portion 17 d can be easily prevented from being positionedat any dead point when the rotating portion is in the stopped state. Inaddition, in the magnet portion 17 d, the magnetic poles 171 arearranged at equal angular intervals in the circumferential direction.This contributes to more easily preventing the circumferential middle ofeach of the magnetic poles 171 from coinciding with the circumferentialmiddle of any of the two coils 141 d when viewed in the verticaldirection. In other words, each magnetic pole 171 of the magnet portion17 d can be more easily prevented from being positioned at any deadpoint when the rotating portion is in the stopped state.

As described above, the number of magnetic element portions 125 is equalto or smaller than the number of magnetic poles 171. This contributes toincreasing the probability that the circumferential middle of anymagnetic pole 171 will be positioned over the circumferential middle ofeach magnetic element portion 125 when the rotating portion stops. Thismakes it easier to prevent each magnetic pole 171 of the magnet portion17 d from being positioned at any dead point when the rotating portionis in the stopped state. In addition, the angle A3 defined between thefirst plane S1 and the second plane S2 is equal to 90 degrees divided bythe number of magnetic poles 171. This contributes to more easilypreventing each magnetic pole 171 of the magnet portion 17 d from beingpositioned at any dead point when the rotating portion is in the stoppedstate.

As described above, the lower surface 221 of the spacer 22 d is arrangedopposite to the upper surface of the coil portion 14 d in the verticaldirection. Thus, in the vibration motor 1 d, the coil 141 d of the coilportion 14 d can be arranged radially closer to the shaft 15 than in avibration motor in which a spacer is arranged radially inside of aplurality of coils arranged around a shaft. This contributes to reducingthe radial dimension of the vibration motor 1 d while limiting areduction in vibrations of the vibration motor 1 d.

As described above, the lower surface 221 of the spacer 22 d is arrangedto be in contact with the upper surface 142 of each of the coils 141 d.This contributes to reducing the vertical dimension of the vibrationmotor 1 d. In addition, if the vibration motor 1 d falls, for example,vertical movement of the coil 141 d is limited, and this contributes topreventing the coil 141 d from being detached from the circuit board 13.Further, a difference between the vertical positions of the uppersurfaces 142 of the coils 141 d can be prevented, and this makes it easyto secure a vertical distance between the coil portion 14 d and themagnet portion 17 d, that is, a gap between the coil portion 14 d andthe magnet portion 17 d.

Note that, in the vibration motor 1 d, the number of magnetic poles 171and the number of magnetic element portions 125 may be modified invarious manners. As illustrated in FIG. 27, the number of magnetic poles171 may alternatively be two. The number of magnetic element portions125 may also alternatively be two. In a modification of the fifthpreferred embodiment illustrated in FIG. 27, the number of the at leastone coil 141 d of the coil portion 14 d is equal to the number ofmagnetic poles 171 of the magnet portion 17 d. This contributes toeasily preventing the circumferential middle of each of the magneticpoles 171 from coinciding with the circumferential middle of any of thecoils 141 d when viewed in the vertical direction. In other words, eachmagnetic pole 171 of the magnet portion 17 d can be easily preventedfrom being positioned at any dead point when the rotating portion is inthe stopped state.

Note that each of the vibration motors 1 and 1 a to 1 d described abovemay be modified in various manners.

The cover portion 11 may alternatively be made of any desirable materialother than metals.

In each of the base portions 12, 12 a, 12 b, and 12 d, the upper surface31 of the base magnetic portion 122 and the upper surface 33 of the basenonmagnetic portion 123 may alternatively be arranged at differentvertical levels in an area where the upper surfaces 31 and 33 arecovered with the circuit board 13. Also, the lower surface 32 of thebase magnetic portion 122 and the lower surface 34 of the basenonmagnetic portion 123 may alternatively be arranged at differentvertical levels. Further, the upper surface of the entire portion of thebase portion 12, 12 a, 12 b, or 12 d which lies between the shaft 15 andthe magnetic element portions 125 and the nonmagnetic element portions127 may not necessarily be arranged at the same vertical level. Forexample, a portion of the upper surface of each of the base portions 12,12 a, 12 b, and 12 d which lies around the shaft 15 may be arranged toproject upward relative to the remaining portion thereof and to be incontact with a lower end portion of the shaft 15, so that the shaft 15can be securely fixed to the base portion 12, 12 a, 12 b, or 12 d.

Note that the shape of each of the base magnetic portion 122 and thebase nonmagnetic portion 123 may be modified in various manners, as longas the base magnetic portion 122 and the base nonmagnetic portion 123include the plurality of magnetic element portions 125 and the pluralityof nonmagnetic element portions 127, respectively, which are arranged inthe circumferential direction, and which are arranged at the positionsopposed to the magnet portion 17 or 17 d in the vertical direction. Alsonote that the shape of each of the magnetic element portions 125 and thenonmagnetic element portions 127, the number of magnetic elementportions 125, and the number of nonmagnetic element portions 127 may bemodified in various manners. For example, in each of the base portion 12illustrated in FIG. 6, the base portion 12 b illustrated in FIG. 17, andthe base portion 12 d illustrated in FIG. 25, each of the magneticelement portions 125 may alternatively be spaced from the magnetic outercircumferential portion 124. Also, each of the nonmagnetic elementportions 127 may alternatively be spaced from the nonmagnetic centralportion 126. In the base portion 12 a illustrated in FIG. 16, each ofthe magnetic element portions 125 may alternatively be spaced from themagnetic central portion 124 a. Also, each of the nonmagnetic elementportions 127 may alternatively be spaced from the nonmagnetic outercircumferential portion 126 a.

The magnetic element portions 125 may not necessarily be arranged atequal angular intervals in the circumferential direction, but anglesdefined between different pairs of adjacent ones of the magnetic elementportions 125 may be different. The nonmagnetic element portions 127 maynot necessarily be arranged at equal angular intervals in thecircumferential direction, but angles defined between different pairs ofadjacent ones of the nonmagnetic element portions 127 may be different.

Each of the base portions 12, 12 a, 12 b, and 12 d may not necessarilybe provided with the base central through hole 128 in which the lowerend of the shaft 15 is fixed. Also, the base peripheral through hole129, which is arranged at a position away from the shaft 15, mayalternatively be defined in the magnetic outer circumferential portion124 or the nonmagnetic outer circumferential portion 126 a. The baseperipheral through hole 129 may not necessarily be provided. The boardperipheral through hole 132 of the circuit board 13 may not necessarilybe provided, either.

The lower surface 221 of each of the spacers 22 and 22 a to 22 d mayalternatively be spaced upward from the upper surface of the coilportion 14 or 14 d, as long as the lower surface 221 is arrangedopposite to the upper surface of the coil portion 14 or 14 d in thevertical direction. The lower surface 221 of each of the spacers 22 and22 a to 22 d may not necessarily be arranged opposite to the uppersurface of the coil portion 14 or 14 d in the vertical direction. Eachof the spacers 22 and 22 a to 22 c may alternatively be arrangedradially inside of the coil 141 of the coil portion 14, that is, betweenthe inner circumferential surface of the coil 141 and the shaft 15. Thespacer 22 d may alternatively be arranged between the shaft 15 and theplurality of coils 141 d of the coil portion 14 d and radially inside ofthe coils 141 d.

In each of the magnet portions 17 and 17 d, the number of magnetic poles171 may be modified appropriately. Also, the magnetic poles 171 may notnecessarily be arranged at equal angular intervals in thecircumferential direction, but angles defined between different pairs ofadjacent ones of the magnetic poles 171 may be different. The number ofmagnetic poles 171 may alternatively be smaller than the number ofmagnetic element portions 125.

In the vibration motor 1 d, the number of coils 141 d of the coilportion 14 d may alternatively be greater than the number of magneticpoles 171 of the magnet portion 17 d.

Attachment and fixing of each member of each of the vibration motors 1and 1 a to 1 d may be achieved in an indirect manner. For example, thecircuit board 13 may alternatively be arranged above the base portion12, 12 a, 12 b, or 12 d with another member intervening between thecircuit board 13 and the base portion 12, 12 a, 12 b, or 12 d. Also,each of the coil portions 14 and 14 d may be attached to the circuitboard 13 with another member intervening therebetween. Also, theattachment of the shaft 15 to the cover portion 11 and the base portion12, the attachment of each of the magnet portions 17 and 17 d to acorresponding one of the rotor holders 16 and 16 a to 16 c, theattachment of each of the eccentric weights 18 and 18 a to acorresponding one of the rotor holders 16 and 16 a to 16 c, the fixingof the cover portion 11 to the base portion 12, and so on may beachieved with an intervention of another member.

Features of the above-described preferred embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

Vibration motors according to preferred embodiments of the presentinvention may be used for various purposes. Vibration motors accordingto preferred embodiments of the present invention are preferably used assilent notification devices in mobile communication apparatuses, suchas, for example, cellular phones.

Features of the above-described preferred embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A vibration motor comprising: a base portion thatextends perpendicularly to a central axis extending in a verticaldirection; a shaft including a lower end fixed to the base portion, andprojecting upward along the central axis; a circuit board above the baseportion; a coil portion attached to the circuit board, and radiallyopposite to the shaft with a gap therebetween; a bearing portionattached to the shaft to be rotatable with respect to the shaft abovethe coil portion; a rotor holder attached to the bearing portion; amagnet portion including a plurality of magnetic poles, and attached tothe rotor holder; an eccentric weight attached to the rotor holder; anda cover portion that covers, at least in part, upper and lateral sidesof the rotor holder and the eccentric weight, and fixed to an upper endof the shaft and an outer edge portion of the base portion; wherein thebase portion includes: a base magnetic portion made of a magnetic metal;and a base nonmagnetic portion made of a nonmagnetic metal, fixed to anedge portion of the base magnetic portion, and extending from the edgeportion of the base magnetic portion perpendicularly to the verticaldirection; the base magnetic portion includes a plurality of magneticelement portions arranged in a circumferential direction, and providedat positions opposed to the magnet portion in the vertical direction;the base nonmagnetic portion is defined b a single continuous monolithicmember which includes a plurality of integrally provided nonmagneticelement portions arranged to alternate with the magnetic elementportions in the circumferential direction, and provided at positionsopposed to the magnet portion in the vertical direction; the basemagnetic portion includes a first boundary portion where the basemagnetic portion is in contact with the base nonmagnetic portion; thebase nonmagnetic portion includes a second boundary portion where thebase nonmagnetic portion is in contact with the base magnetic portion;an area where the first and second boundary portions are in contact witheach other is defined as a boundary portion; and the base magneticportion and the base nonmagnetic portion do not overlap with each otherat any position outside of the boundary portion when viewed in thevertical direction the base magnetic portion further includes a magneticouter circumferential portion that surrounds an outer periphery of thebase nonmagnetic portion; each of the magnetic element portions projectsradially inward from the magnetic outer circumferential portion; thebase nonmagnetic portion further includes a nonmagnetic central portionto which the lower end of the shaft is fixed; and each of thenonmagnetic element portions projects radially outward from thenonmagnetic central portion.
 2. The vibration motor according to claim1, wherein the base magnetic portion and the base nonmagnetic portion donot overlap with each other even at the boundary portion when viewed inthe vertical direction.
 3. The vibration motor according to claim 1,wherein the base magnetic portion and the base nonmagnetic portionoverlap with each other at the boundary portion when viewed in thevertical direction.
 4. The vibration motor according to claim 1, whereinan upper surface of the base magnetic portion and an upper surface ofthe base nonmagnetic portion are arranged at a same vertical level overan area where an upper surface of the base portion is covered with thecircuit board.
 5. The vibration motor according to claim 4, wherein alower surface of the base magnetic portion and a lower surface of thebase nonmagnetic portion are arranged at a same vertical level.
 6. Thevibration motor according to claim 5, wherein a radially inner endportion of each of the magnetic element portions is opposite to themagnet portion in the vertical direction.
 7. The vibration motoraccording to claim 6, wherein a circumferential width of a portion ofeach magnetic element portion which is opposed to the magnet portion inthe vertical direction is equal to or smaller than a circumferentialwidth of each magnetic pole of the magnet portion at any radialposition.
 8. The vibration motor according to claim 7, wherein acircumferential width of each of the magnetic element portions decreasesin a radially inward direction.
 9. The vibration motor according toclaim 5, wherein the base nonmagnetic portion further includes anonmagnetic outer circumferential portion arranged to surround an outerperiphery of the base magnetic portion; each of the nonmagnetic elementportions projects radially inward from the nonmagnetic outercircumferential portion; the base magnetic portion further includes amagnetic central portion to which the lower end of the shaft is fixed;and each of the magnetic element portions projects radially outward fromthe magnetic central portion.
 10. The vibration motor according to claim9, wherein a circumferential width of each of the magnetic elementportions decreases in a radially outward direction.
 11. The vibrationmotor according to claim 9, further comprising a spacer attached to theshaft between the bearing portion and the coil portion, and including anupper surface in contact with a lower surface of the bearing portion,wherein a lower surface of the spacer is opposite to an upper surface ofthe coil portion in the vertical direction.
 12. The vibration motoraccording to claim 11, wherein a number of magnetic poles is a multipleof two.
 13. The vibration motor according to claim 12, wherein a numberof magnetic element portions is equal to or smaller than the number ofmagnetic poles.
 14. The vibration motor according to claim 13, whereinthe magnetic poles are arranged at equal angular intervals in thecircumferential direction.
 15. The vibration motor according to claim14, wherein the number of magnetic element portions is equal to thenumber of magnetic poles; and the magnetic element portions are arrangedat equal angular intervals in the circumferential direction.
 16. Thevibration motor according to claim 1, wherein the base portion furtherincludes a base projecting portion that projects radially outward fromthe cover portion; and an angle defined between a first plane and asecond plane is equal to 90 degrees divided by a number of magneticpoles of the magnet portion, the first plane including the central axisand a circumferential middle of the base projecting portion, the secondplane including the central axis and a circumferential middle of one ofthe magnetic element portions that is closest to the first plane in thecircumferential direction.
 17. The vibration motor according to claim16, wherein the coil portion is defined by a single annular coil insideof which the shaft is arranged.
 18. The vibration motor according toclaim 16, wherein the coil portion includes at least one coil arrangedaround the shaft; and a number of the at least one coil is equal to orsmaller than the number of magnetic poles of the magnet portion.
 19. Thevibration motor according to claim 18, wherein the number of the atleast one coil is two; the number of magnetic poles of the magnetportion is six; and a number of magnetic element portions is three. 20.The vibration motor according to claim 18, wherein the number of the atleast one coil is equal to the number of magnetic poles of the magnetportion.
 21. The vibration motor according to claim 18, wherein each ofthe at least one coil is circumferentially displaced from one of themagnetic poles by an angle equal to 2M−1 times an angle obtained bydividing 90 degrees by the number of magnetic poles, where M is anatural number equal to or smaller than twice the number of magneticpoles.
 22. The vibration motor according to claim 16, wherein the baseportion further includes a base central through hole passingtherethrough in the vertical direction; and the lower end of the shaftis fixed in the base central through hole.
 23. The vibration motoraccording to claim 22, wherein an upper surface of an entire portion ofthe base portion which lies between the shaft and the magnetic elementportions and the nonmagnetic element portions is arranged at a samevertical level.
 24. The vibration motor according to claim 23, whereinthe base portion further includes a base peripheral through hole at aposition away from the shaft; and the circuit board includes a boardperipheral through hole that overlaps with the base peripheral throughhole when viewed in the vertical direction.
 25. The vibration motoraccording to claim 24, wherein one of the base nonmagnetic portion andthe base magnetic portion surrounds an outer periphery of another one ofthe base nonmagnetic portion and the base magnetic portion; and the baseperipheral through hole is defined in the other one of the basenonmagnetic portion and the base magnetic portion.